Tryptase

In brief

What tryptase is, in plain terms

A mast cell is a long-lived immune cell that sits in tissues meeting the outside world, the skin, the airway lining, the gut wall, packed with granules the way a cell might be packed with ammunition. When it is triggered it empties those granules into the surrounding tissue in seconds. Histamine is the famous content. Tryptase is the most abundant protein by weight ³¹, and it is a protease, which simply means an enzyme that cuts other proteins. Specifically it is a serine protease, named for the serine amino acid in the pocket where the cutting happens, and trypsin-like, meaning it cuts next to the basic amino acids lysine and arginine, the same preference that the digestive enzyme trypsin has ^1,32.

G. G. Glenner and L. A. Cohen demonstrated a trypsin-like enzyme in mast cells histochemically, meaning by a color reaction on a tissue section, in a short 1960 paper in Nature; the record carries no abstract, so it is cited here for the existence and date of the observation ³³. Twenty-one years later Lawrence Schwartz, Robert Lewis and K Frank Austen purified it from dispersed human lung mast cells and described what it was: an enzyme of apparent mass 120,000 to 140,000 by gel filtration, resolving on denaturing gels into subunits of 37,000 and 35,000 in equal molar proportion, consistent with a tetramer of about 144,000, with all four subunits labeled by an active-site probe ¹. They calculated that one million mast cells hold about 6 to 19 micrograms of the enzyme, which is an enormous amount of a single protein for a cell to carry, and the reason tryptase makes a usable blood marker at all ¹.

The structure explains almost everything else about it. In 1998 Pedro Pereira and colleagues solved the crystal structure of human beta-tryptase at 3 angstroms and found four nearly identical (quasi-equivalent) subunits arranged in a flat square ring, their four catalytic centers all pointed inward toward an oval central pore ⁶. Access to the active sites is therefore through a hole. Small peptides fit; large proteins do not. That single geometric fact accounts for the enzyme's most unusual property, which is that it resists every endogenous protease inhibitor the body makes, because those inhibitors are themselves proteins ⁶. The same structure suggested that heparin chains might bridge two adjacent subunits across an elongated patch of positive charge, a proposed explanation for how the ring is held together ⁶.

Heparin is not incidental; it is the switch. Schwartz and Bradford showed in 1986 that tryptase separated from heparin at body temperature in buffer or in plasma lost half its activity within 6 to 8 minutes, while heparin-bound enzyme retained nearly full activity for two hours ⁵. Chromatography showed that active enzyme behaved as a species of about 132,000 and inactivated enzyme as one of about 34,000, with the protein itself undamaged on gels: the enzyme switches off by falling apart, not by being destroyed ⁵. The authors concluded that storing heparin and tryptase together in the granule most likely plays a major role in regulating the enzyme after it is secreted ⁵; how long the pair actually holds together in human tissue was not measured. Yoshihiro Fukuoka and Schwartz later showed in test-tube experiments that the picture is not quite binary: under slightly acidic conditions (pH 6, of the kind associated with inflamed tissue), with heparin or another long negatively charged molecule present, the single subunits themselves cut small peptides, and unlike the tetramer they are inhibited by soybean trypsin inhibitor, bovine pancreatic trypsin inhibitor, antithrombin III and alpha-2-macroglobulin ³⁴.

The genes at 16p13.3, and the alpha/beta problem

The tryptase genes sit in a small cluster at band 16p13.3, near the tip of the short arm of chromosome 16 ³. Mapping it took work, because the genes are nearly identical to one another and lie in tandem, one after another along the chromosome. In 1999 Pallaoro and colleagues sequenced bacterial artificial chromosome clones (stretches of human DNA copied in bacteria so that they can be sequenced) from the region and found three known beta-tryptases (betaI, betaII, betaIII), an alpha-like gene, and a pair of novel hybrid genes; they concluded that betaII and betaIII are probably alleles (alternative versions of a gene) at one locus (a gene's position on the chromosome), betaI and alphaII alleles at a neighboring one, and that the clones contained at least three non-allelic tryptase genes ³. In modern naming, one locus is TPSAB1, which may carry either an alpha or a beta sequence, and the neighboring locus, the one next to gamma-tryptase, is TPSB2, which carries beta ^4,8. The following year the same group described gamma-tryptase, a separate relative lying between a calcium channel gene (CACNA1H) and the beta genes, with a catalytic domain about 48 percent identical to the mast cell tryptases and, unusually, a water-repelling (hydrophobic) segment at the end of the protein chain that probably anchors it in a membrane; they also catalogued at least four tryptase-like pseudogenes (gene-like sequences that no longer make protein) in the cluster, including one, mastin, that is expressed in dogs but not in humans ⁴.

Because the genes are so alike, people differ in how many of each they carry, and the differences are large and ordinary. In 2002 Soto and colleagues genotyped 274 individuals and found that 80 of them, 29 percent, had no alpha gene at all and carried four beta genes instead; 21 percent were alpha-alpha-beta-beta and 50 percent alpha-beta-beta-beta, giving an overall alpha allele frequency of only 0.23 ⁸. Alpha deficiency affected 45 percent of the white subjects in the sample and a much lower proportion of African-American and Asian subjects ⁸. This is worth stating plainly: more than a quarter of the people surveyed had no gene for one of the two named forms of tryptase, and no disease has been tied to it ⁸. The total number of active tryptase genes does, however, go with small differences in tryptase level, and in two studies with how often anaphylaxis occurred and with how well asthma responded to treatment ^24,37.

Alpha-tryptase is strange, and that strangeness was solved structurally in 2002. Marquardt and colleagues solved the crystal structure of mature human alpha-1-tryptase at 2.2 angstroms and found a frame-like tetramer that, surprisingly, did not need heparin for stability, but in which the stretch of the protein chain that normally cradles the target (amino acids 214 to 219, the Ser214-Gly219 segment) was kinked, blocking one side of the groove where the target binds (the non-primed subsites) ⁷. The authors blamed a single amino acid, an aspartate at position 216 (Asp216), and noted that activity could in principle be generated by an induced fit, in which binding of the target forces the enzyme into working shape ⁷. The practical reading is that alpha-only tetramers are not productive proteases, and for years this made alpha-tryptase look like an evolutionary spare part.

That reading was overturned in 2019. Quang Le, Jonathan Lyons, Lawrence Schwartz and colleagues showed in laboratory experiments that in anyone who makes alpha, mixed tetramers of two alpha and two beta subunits (protomers) form naturally ²⁰. Unlike either pure form, these mixed tetramers switch on protease-activated receptor 2, a receptor on smooth muscle, nerves and the lining of blood vessels, and they cut the vibration-sensing receptor EMR2, which in the experiments made mast cells susceptible to degranulating when shaken ²⁰. The alpha subunits appear to change the behavior of their beta neighbors from a distance (an allosteric effect), giving the mixed tetramer targets neither parent has ²⁰. One of the authors was a Genentech scientist; the company was developing an antibody against tryptase at the time ^20,37. Alpha-tryptase is therefore not inert; it changes what the enzyme does, which supplies a candidate mechanism for the clinical associations in the hereditary alpha-tryptasemia section below, though the experiments do not test those associations in patients.

Even within the normal range, the tryptase locus explains the number. A 2026 Slovenian study genotyped 295 people with systemic reactions to Hymenoptera stings (bees, wasps, hornets and ants), 140 with large local reactions (big swelling around the sting only) and 29 who were sensitized without symptoms (allergy antibodies on testing but no reactions), excluding anyone with the mastocytosis mutation KIT D816V or hereditary alpha-tryptasemia, and found that the count of active tryptase alleles correlated with the baseline level (r = 0.34, p < 0.0001) while every value stayed inside the normal range ²⁴. In the same cohort, people carrying four active beta alleles were less likely to have had anaphylaxis than those carrying two or three (26.7 percent versus 42.3 percent, p = 0.024), an association, not a demonstrated cause ²⁴.

The whole history, including the reversals

The arc of this subject runs from a stain on a slide to a copy-number test, and it contains many reversals, among them: alpha-tryptase turning out not to be the main thing in blood, alpha-tryptase turning out not to be inert, a high baseline turning out usually not to mean disease, a genetic trait turning out not to carry the symptom list first attributed to it, and a normal tryptase after death turning out to be the exception rather than the rule. Each is in the timeline below in its own words, and they are gathered in the section on what was believed and is not.

What makes the story unusual is that overlapping groups did the laboratory work and made the clinical claims over four decades. Lawrence Schwartz is an author on the 1981 purification, done with K Frank Austen as senior author ¹; from Virginia Commonwealth University he is also an author on the 2016 discovery of hereditary alpha-tryptasemia, the 2019 heterotetramer paper, the consensus criteria for mast cell activation syndrome and the 2021 review defending them ^13,18,20,38. That continuity is a strength for the biochemistry. It also means that in the diagnostic-criteria literature the same names recur on the consensus documents and on the studies that test them, which a reader weighing those studies should know. The commercial interests are concrete and are stated where they apply: Blueprint Medicines, which makes the KIT inhibitor avapritinib, employed authors of the PIONEER anaphylaxis analysis and of the PROSPECTOR screening study ^39,40, and Genentech employees ran the anti-tryptase antibody program from discovery to the failed asthma trial ^31,37,41,42.

How the test is actually done, and the window that decides it

Two samples, not one. The acute sample should be drawn when the level is highest, which the 1989 kinetic study placed at 1 to 2 hours after the trigger, and a perioperative series confirmed with a median time to peak of 1.34 hours ^12,14; a 2023 review places the useful window within 4 hours of the event, and a 2025 gastroenterology practice update advises 1 to 4 hours after a flare ^11,78. The baseline sample is drawn later, when the person is well and at least 24 hours after the event ¹¹, and it is the comparison between the two that carries the information. A single acute value in isolation can only be interpreted if it is extremely high, because the population range is wide, from under 1 to 30.7 micrograms per liter in 420 randomly sampled adults, and a person's own normal might be anywhere in it ⁹.

The routine assay measures total tryptase, meaning the continuously secreted precursor plus any mature enzyme released by degranulation, together in one number. The reason it works at all is the difference in half-life. Histamine peaks within 5 to 10 minutes and is back to baseline within 15 to 60 minutes, which in practice means it is gone before the patient reaches a laboratory; tryptase peaks later and falls with a half-life of about 2 hours, so a sample taken in the emergency department still carries the signal ¹². The sample is also forgiving: four freeze-thaw cycles did not reduce the measured level, and more than half of the endogenous enzyme was still detectable after four days at room temperature or at body temperature ¹².

Separating the two pools directly is possible but has not proved useful. The B12 capture assay measures both forms, the G5 assay mainly mature beta-tryptase, and the ratio is at least 10 in most patients with systemic mastocytosis at rest and near 1 in acute anaphylaxis ³⁶. When a 2019 study tested this in 102 perioperative patients, a detectable mature tryptase was less sensitive than the total-tryptase equation, especially when the acute total was below 16 micrograms per liter ⁵⁹, and in a 2022 study mature tryptase was non-contributory at baseline in both hereditary alpha-tryptasemia and indolent systemic mastocytosis ⁶⁵. On this evidence it adds little to the routine total-tryptase test ^59,65.

A point that gets lost: anaphylaxis is a clinical diagnosis, and tryptase is confirmatory. The United States practice parameters treat it that way. The 2020 update makes epinephrine the first-line drug and keeps patients under observation until symptoms have resolved ⁷⁹; the 2023 update adds that tryptase is important for confirming anaphylaxis and for finding an underlying mast cell disorder, and that adults with severe sting reactions or recurrent unexplained anaphylaxis should be considered for evaluation for mastocytosis, including a bone marrow biopsy ⁷¹. Neither makes treatment wait for a laboratory result ^71,79. In a 1992 series of 13 children and adolescents with fatal or near-fatal food anaphylaxis, the six who died had symptoms within 3 to 30 minutes of eating and only two received epinephrine in the first hour, while all the survivors but one received it within 30 minutes ⁸⁰. Nothing about a tryptase level should delay that injection.

• Serum total tryptase, acute and baselineAn immunoassay measuring the precursor and mature forms together; the acute sample is compared with the same person's own baseline drawn later ^13,14.To document mast cell activation in suspected anaphylaxis, and to screen for mastocytosis when measured at baselineAgainst the consensus rule that the acute level must exceed 1.2 times baseline plus 2 micrograms per liter, sensitivity was 78 percent and specificity 91 percent, with positive predictive value 98 percent and negative predictive value 44 percent, in 71 patients with paired samples investigated for anaphylaxis under general anesthesia, 60 with anaphylaxis and only 11 controls ¹⁴; an independent, retrospective perioperative series of 102 patients gave 75 percent sensitivity, 86 percent specificity, 94 percent positive and 53 percent negative predictive value ⁵⁹. Pooled across 24 studies of tryptase in a 2025 meta-analysis, sensitivity was 0.49 and specificity 0.82 ²¹.Food-triggered anaphylaxis often does not raise it, samples drawn too early or too late miss the peak, and a single level without a baseline cannot be interpreted ^12,23,25. A negative result does not exclude anaphylaxis: the diagnosis is clinical ⁷⁹.
• Tryptase genotyping by droplet digital PCRA copy-number assay by droplet digital PCR (polymerase chain reaction, a DNA-copying test, run in thousands of tiny droplets so that gene copies can be counted exactly) that counts alpha- and beta-tryptase sequences at TPSAB1 and TPSB2, used to diagnose hereditary alpha-tryptasemia ^18,19.To explain an elevated baseline tryptase, and to set an individualized upper limit of normal before a bone marrow biopsy is consideredCopy number is strongly and dose-dependently related to the baseline level; modeling from it generates personal reference values, and in the absence of extra alpha copies a baseline above 11.4 ng/mL frequently identifies indolent clonal mast cell disease ⁶⁹.On its own it says little about symptoms. In a random biorepository population the only consistent phenotypic marker of the trait was the raised tryptase itself, with no difference in symptoms from controls ⁶³, although a 2026 questionnaire study in allergy patients found a heavier reported symptom load in carriers ⁶⁴. And a baseline below 8 ng/mL does not exclude it: 4 of 15 patients with the trait in a 2026 asthma cohort were below that threshold ⁸⁹.
• KIT D816V in peripheral bloodA sensitive polymerase chain reaction (DNA-copying) assay for the single activating mutation that drives nearly all adult systemic mastocytosis ^27,54.Alongside tryptase, to decide who needs a bone marrow biopsyDetected in peripheral blood in 78 of 83 adults with systemic mastocytosis (94 percent) and in 3 of 4 with cutaneous disease, with no positives among clinically relevant controls; of 27 patients whose tryptase was low, 26 were mutation positive ²⁷. In people presenting with severe mediator symptoms rather than known mastocytosis the yield is far lower: in a 2026 Spanish series of 1,204 such patients without skin lesions, blood testing found the mutation in only 29 percent of those shown to have clonal disease ²⁸.It is a test for clonal disease, not for activation, and in children it behaves differently: in 68 children with cutaneous mastocytosis only 7 (10.3 percent) were positive in blood ⁹⁴.
• Mature (beta) tryptase assayThe G5-capture assay, which measures mainly the mature tetramer released on degranulation rather than the continuously secreted precursor ³⁶.Research and specialist settings, to separate activation from mast cell burdenIn mastocytosis at rest the total-to-mature ratio exceeds 10, while in acute anaphylaxis it approaches 1, which separates the two states cleanly in principle ³⁶.In practice it adds little. A detectable mature level was less sensitive than the total-tryptase equation, particularly when the acute total was below 16 micrograms per liter, and mature tryptase was non-contributory at baseline in both hereditary alpha-tryptasemia and indolent systemic mastocytosis ^59,65.

The 20 percent plus 2 formula, and how often it is actually met

The rule is arithmetic, not judgment. An acute total tryptase counts as evidence of mast cell activation if it exceeds 1.2 times the person's own baseline plus 2 micrograms per liter: a 20 percent rise, plus 2. It was set out in the 2010 working conference whose consensus proposal was published in 2012, as the second of three criteria for a mast cell activation syndrome, alongside typical episodic symptoms involving at least two organ systems and a response to drugs that block mast cell mediators ¹³. The additive 2 exists because a 20 percent rise on a baseline of 3 is within assay and biological noise, while a 20 percent rise on a baseline of 40 is not.

It has been validated twice, both times in the operating room, where the timing of the reaction is known to the minute. In 82 patients investigated for suspected anaphylaxis during general anesthesia, of whom 60 met World Allergy Organization criteria, the equation gave sensitivity 78 percent, specificity 91 percent, positive predictive value 98 percent and negative predictive value 44 percent ¹⁴. In an independent French series of 102 perioperative patients it was the best of four tested algorithms, with sensitivity 75 percent, specificity 86 percent, positive predictive value 94 percent, negative predictive value 53 percent and a Youden index of 0.61 ⁵⁹. Read those four numbers together: when the formula is met it is almost always right, and when it is not met it tells you almost nothing.

Outside the operating room the sensitivity is worse, because the trigger and the timing are not controlled. In 102 emergency department patients with clinical anaphylaxis, sampled at 1 to 2 hours, tryptase was simply not raised in 36.3 percent, and in nearly two-thirds of those the acute value was indistinguishable from the person's own baseline ²⁵. In 97 adults presenting with acute allergic reactions, plasma histamine was above 10 nanomoles per liter in 42 but total tryptase was above 15 ng/mL in only 20, and the authors concluded that the discrepancy pointed to basophil rather than mast cell involvement in many of them ⁸¹.

The formula also fires in people who are not reacting. Allyson Mateja and colleagues took 93 people with at least two baseline measurements, modeled the ordinary variability of baseline tryptase, and found that 9.7 percent met the 20 plus 2 rule on two routine baseline samples with no immediate hypersensitivity symptoms at all. That false-positive rate rose with the baseline level: 18 percent in people with hereditary alpha-tryptasemia, 30 percent in indolent systemic mastocytosis, 25 percent in both together. A ratio of acute to baseline above 1.685 jointly maximized sensitivity and specificity and significantly improved specificity in the groups with high baselines ⁶⁵. The 2019 refinement most often cited in practice is the diagnostic algorithm published by Valent and colleagues the same year, which places the formula inside a sequence that first asks whether the episode was systemic and recurrent, and then whether severe allergy or mastocytosis explains it, before any syndrome label is applied ⁸².

A 2026 review summarizing where this stands describes the formula as validated and the recognition of hereditary alpha-tryptasemia as having refined the algorithms around it, while stressing that interpretation depends on knowing both the baseline and the genotype ⁸³.

Baseline above 20 ng/mL: the mastocytosis criterion and the mutation beside it

Systemic mastocytosis is a clonal neoplasm of mast cells, meaning the cells are the descendants of one mutated progenitor and accumulate where they should not. Its diagnosis rests on one major criterion, dense multifocal aggregates of at least 15 mast cells in bone marrow or another extracutaneous organ, and four minor criteria: abnormal spindle-shaped morphology, aberrant expression of CD25, CD2 or CD30 on mast cells, a KIT point mutation at codon 816, and a baseline serum tryptase above 20 ng/mL ^16,17. The major criterion plus one minor, or three minor criteria, make the diagnosis. Both the World Health Organization's fifth edition and the parallel International Consensus Classification published in 2022 retain this structure ^17,66.

The tryptase threshold earns its place because the level tracks mast cell burden. In 59 patients studied with bone marrow immunohistochemistry, the degree of infiltration correlated with the serum level at r = 0.8; medians were 10 ng/mL in cutaneous mastocytosis and 67 ng/mL in systemic disease, values above 900 ng/mL occurred in mast cell leukemia and smoldering disease, and the three patients with isolated bone marrow mastocytosis were all below 20 ⁵². That last group is the warning inside the same dataset: the threshold is a population rule with individual exceptions at both ends.

The mutation is the more specific test. KIT D816V was present in 93 percent of adults with indolent and aggressive systemic mastocytosis, though in only 29 percent of the well-differentiated variant ⁵⁴, and with a sufficiently sensitive assay it can be found in peripheral blood in 78 of 83 adults with systemic mastocytosis (94 percent) and in 3 of 4 with cutaneous disease, with no false positives among clinically relevant controls ²⁷. Critically, of 27 of those patients whose tryptase was below 20 ng/mL, 26 were still mutation positive ²⁷. Blood mutation testing finds disease that the tryptase threshold misses.

This matters most in venom allergy. Among 379 people with systemic reactions to Hymenoptera stings, 44 (11.6 percent) had a baseline tryptase above 11.4 ng/mL, and of the 34 who underwent bone marrow examination, 21 had indolent systemic mastocytosis and 9 had monoclonal mast cell activation syndrome: every patient with anaphylaxis in that group had one of the two ⁸⁴. A Slovenian study then showed the reverse exposure. Among 374 patients with venom allergy and no overt mastocytosis, 351 had a normal baseline tryptase, and yet KIT D816V was found in 8 percent of them, concentrated in the most severe grade IV reactions (18.2 percent versus 1.8 percent in lower grades). Within the normal-tryptase group the mutation carried an odds ratio of 10.25 (95 percent confidence interval 3.75 to 36.14) for severe anaphylaxis, and patients who carried it were more likely to lose consciousness and less likely to have any skin involvement ²⁶.

The level is not only a mast cell count. In 914 patients with hematological disease, elevated tryptase clustered in myeloid rather than lymphoid neoplasms, with levels above 15 ng/mL in 38 percent of acute myeloid leukemia, 34 percent of chronic myeloid leukemia and 25 percent of myelodysplastic syndrome, and the highest values, often above 1000 ng/mL, in advanced mastocytosis and core-binding-factor leukemias ²⁹. In hypereosinophilic syndrome a raised tryptase marked the myeloproliferative variant carrying the FIP1L1-PDGFRA fusion, a subgroup with tissue fibrosis and worse survival in which all six patients treated with imatinib responded ⁵³. An unexplained high baseline tryptase in an adult is a hematology question as much as an allergy one, a point a 2026 joint allergy-hematology cohort makes directly: of 24 adults taken to marrow and sequencing, all 10 with non-allergic presentations had a clonal mast cell disorder, against 1 of 14 presenting with anaphylaxis, and median baseline tryptase was 22.4 ng/mL in those with mastocytosis against 3.2 ng/mL in those without ⁸⁵.

Whether treating the clone reduces anaphylaxis is still open. In the PIONEER trial of avapritinib, a selective KIT D816V inhibitor, in moderate-to-severe indolent systemic mastocytosis, 13 of 212 patients (6.1 percent) had anaphylaxis during screening or treatment, and during the randomized placebo-controlled period the rates were 4 of 141 (2.8 percent) on avapritinib and 3 of 71 (4.2 percent) on placebo: numbers too small to show a difference either way, as the authors state ³⁹.

Hereditary alpha-tryptasemia: a common trait, and what it does and does not explain

In 2016 Jonathan Lyons and colleagues reported that germline duplications and triplications of the alpha-tryptase-encoding sequence at TPSAB1 segregated with inherited high baseline tryptase across 35 families, with a dose effect: people with three copies on an allele had higher levels and more symptoms than those with two ¹⁸. In two further cohorts totaling 172 people, elevated baseline tryptase was associated exclusively with such duplications ¹⁸. The trait was named hereditary alpha-tryptasemia, it is inherited as a dominant, and it is common: 5.6 percent of 125 healthy volunteers and 5.3 percent of 398 non-atopic disease controls in the American series ⁶¹, 5 percent of an unselected British birth cohort of 432 ¹⁹, 7.5 percent of a random American biorepository population ⁶³, and 4.4 percent of Austrian controls ⁶². About one person in twenty.

It is also the usual answer to the question the test poses. Among patients with Hymenoptera venom allergy and a raised baseline, the trait accounted for 15 of 23 elevations, and together with KIT D816V explained 20 of 23 ²⁶; a 2025 review puts its share of all elevated baselines as high as 72 percent ⁸⁶. The mechanism was worked out in 2023: the extra TPSAB1 copies have co-inherited a linked overactive promoter element, so the replicated loci overexpress ordinary alpha-tryptase protein ⁶⁹.

The original 2016 report attached a symptom list to the trait, including flushing, itch, dysautonomia, irritable bowel symptoms, chronic pain and joint hypermobility ¹⁸, and that list spread widely. It did not survive an unselected sample. Madeleine Chollet and Cem Akin genotyped a random biorepository population and clinic patients, interviewed and examined carriers and controls, and found no difference in clinical symptoms or medical history and no difference in urinary mast cell activation products; elevated baseline tryptase was the only consistent phenotypic marker of the trait ⁶³. A British series of 70 referred patients with the trait found urticaria or angioedema in 51 percent, flushing in 41 percent, food intolerances in 39 percent and altered bowel habit in 36 percent, but no excess of symptoms in those with triplications or quintuplications over those with duplications, and some first-degree relatives with the same genotype and the same high tryptase were asymptomatic; the authors concluded that the trait has variable penetrance and may modify the expression of multifactorial allergic disease rather than cause specific phenotypes ¹⁹. These are referral cohorts and random-population cohorts giving different answers, which is exactly what selection by symptom produces.

Where the association has held up is severity. In the 2021 American series the trait was associated with grade IV venom anaphylaxis, the most severe category, at a relative risk of 2.0 (p < 0.05); it was found in 17 percent of idiopathic anaphylaxis (p = 0.006) and 12.2 percent of systemic mastocytosis (p = 0.03); and among patients with mastocytosis, carrying it as well raised the relative risk of systemic anaphylaxis to 9.5 (p = 0.007) ⁶¹. The same paper supplied a mechanism in vitro: pooled mature tryptases induced protease-activated-receptor-2-dependent permeability across human umbilical vein endothelial cells, while alpha or beta homotetramers did not ⁶¹. An independent Austrian cohort of 180 mastocytosis patients found the trait in 17.2 percent against 4.4 percent of controls, with hymenoptera venom hypersensitivity and severe cardiovascular reactions far more frequent in carriers, and confirmed the finding in a separate validation cohort ⁶². A 2023 study extended the association to food: in two cohorts totaling 119 people, those with any alpha-tryptase had a higher prevalence of food-triggered anaphylaxis (p = 0.026), and in the oral food challenge cohort 20 of 31 subjects with alpha-tryptase had a severe reaction against 1 of 6 with beta-tryptase only, a difference that did not reach significance at p = 0.066 while the severity scores did (p = 0.003) ⁸⁷.

The 2022 refinement that changed practice is the copy-number-adjusted threshold. Chovanec, Lyons and colleagues modeled baseline tryptase against TPSAB1 replication number and generated individualized upper limits of normal, with two consequences. In someone without the trait, a baseline above 11.4 ng/mL, well below the classical 20 ng/mL mastocytosis criterion, frequently identifies indolent clonal mast cell disease. In someone with the trait, a level above 100 ng/mL, which would ordinarily prompt a bone marrow biopsy, can be within that person's normal limits ⁶⁹. A 2025 review sets out how this is applied: tryptase genotyping is required when assessing the World Health Organization minor criterion in patients who do not meet the major criterion, and a correction factor is applied before deciding whether a patient with the trait meets the bone marrow mastocytosis cutoff of 125 ng/mL or the B-finding of 200 ng/mL ⁸⁸.

Two 2026 findings add to the picture and complicate the threshold. In 181 patients with severe allergic asthma treated with omalizumab across Slovenian and British centers, the trait was present in 20 percent of those with a poor clinical response against 5 percent of responders, odds ratio 4.6 (95 percent confidence interval 1.5 to 12.3, p = 0.0068), holding up in multivariable analysis at 4.56; notably, 4 of the 15 carriers had a baseline tryptase below 8 ng/mL, so the usual screening cutoff would have missed them ⁸⁹. And in the gut, where carriers most often complain, a study of 854 biobanked inflammatory bowel disease samples with spatial transcriptomics and mass cytometry found higher mast cell abundance and higher expression of MRGPRX2, a receptor that triggers mast cells without involving IgE, in carriers ⁹⁰. A study of 153 people with celiac disease or non-celiac gluten sensitivity found the trait in 9, all of whom had ongoing symptoms despite a gluten-free diet, with duodenal mast cell counts of 27.3 per high-power field against 22.0 in other celiac patients and 18.4 in controls ⁹¹. These are small, mechanistic and associational; they do not establish that the trait causes gastrointestinal disease ⁹².

The mast cell activation syndrome label, and the dispute about it

The clinical problem is real and predates the label. Patients present with recurrent episodes of flushing, hives, abdominal pain, diarrhea, lightheadedness and sometimes frank anaphylaxis, with no allergen found and no mastocytosis on biopsy. Matthew Hamilton and colleagues described 18 such patients prospectively in 2011: 94 percent had abdominal pain, 89 percent dermatographism, 89 percent flushing, all had at least one laboratory result showing raised mast cell mediators, and 67 percent had complete or major regression of symptoms on drugs targeting those mediators, while the number of mast cells in their gut biopsies was no different from healthy controls ⁹⁵.

Two sets of criteria exist, and they disagree about how many people qualify. The consensus criteria, first proposed by Akin, Valent and Metcalfe in 2010 and formalized by a working conference in 2012, require all three of: typical recurrent systemic symptoms involving at least two organ systems; an event-related rise in serum tryptase meeting the 20 percent plus 2 rule, or an equivalent rise in another mast cell mediator; and a response to mast-cell-directed treatment ^13,55. A 2019 algorithm placed those criteria inside a sequence that rules out severe allergy and mastocytosis first ⁸², and the authors of the consensus position have defended it repeatedly in print, arguing that alternative criteria lack specificity and validation and that patients given a misdiagnosis are denied the investigation of whatever is actually wrong ^38,96. The AAAAI work group report takes the same line, framing its criteria as deliberately specific so as to avoid overdiagnosis ⁹⁷.

The alternative, published in 2020 by 42 authors and labeled consensus-2, holds the opposite. It accepts a much wider range of mast cell mediators and symptom patterns, argues that the tryptase requirement underdiagnoses a prevalent and treatable condition, estimates prevalence at up to 17 percent of the general population, and concludes that until better research exists, diagnosis by either proposal is valid, reasonable and helpful ⁶⁰. A 2026 six-year review from the same group argues that the feared overdiagnosis has not materialized and that the wider criteria have brought effective treatment to patients previously labeled with somatization or unexplained inflammatory syndromes, while conceding that the research remains in early stages and that objective assessment of treatment response is difficult ⁷⁷. A 2026 review from a different group makes a biologically serious version of the same objection: mediator release can occur through several mechanisms without tryptase being released, so a tryptase-anchored definition will necessarily miss some real mast cell activation ⁹⁸.

The honest statement of the disagreement is that the two camps are not measuring the same thing. The consensus criteria are built to be specific and will therefore exclude people who have mast cell-driven symptoms with a tryptase that does not move; the consensus-2 criteria are built to be inclusive and will therefore include people whose symptoms have another cause. Neither estimate of prevalence, the implied rarity of one or the 17 percent of the other, rests on a population study designed to settle it.

What can be counted is how often the tryptase criterion is met in people who are investigated for the syndrome, and the answer is: not often. At a Swedish center, 703 consecutive adults referred on suspicion of a mast cell disorder were evaluated with history, allergy testing, ultrasensitive KIT D816V analysis and, where indicated, bone marrow examination. Thirty-one had confirmed idiopathic mast cell activation syndrome, a prevalence of 4.4 percent of the referred population; the hereditary alpha-tryptasemia trait was found in three patients with baselines above 8 ng/mL ⁷². A Turkish cohort of 21 adults with non-clonal mast cell activation syndromes, 85.7 percent of them women with a mean age of 50.1 years, documented the 20 percent plus 2 rise in all 21 during follow-up, with normal or only mildly raised baselines and no KIT mutation; after full assessment only 6 were classified as idiopathic and the rest as secondary to a comorbidity ⁹⁹. A French pediatric cohort of 44 children with non-mastocytosis mast cell activation disorders could classify only 8 as idiopathic mast cell activation syndrome, the other 36 falling into a category explicitly named not otherwise specified because they did not meet all three criteria ⁹³.

A 2026 World Allergy Organization survey of allergists and clinical immunologists across regions put a number to the bottleneck. Everywhere, clinicians reported a substantial and consistent gap between patients suspected of the syndrome and patients who met all the criteria; documenting a dynamic tryptase rise and accessing urinary mast cell mediator metabolites were named as the principal obstacles; and the gap persisted even in regions with good laboratory access, which the authors read as evidence that structural limitations and diagnostic overextension coexist ⁷⁶. Management in practice was predominantly empiric and symptom-driven, often started without complete diagnostic confirmation ⁷⁶.

One clinically useful consequence of the dispute: the drugs used are mostly the same whichever criteria are applied, and most are old, cheap and safe. H1-antihistamines, H2-blockers, leukotriene receptor antagonists and cromolyn were sufficient in the French pediatric cohort to produce a marked reduction in symptoms ⁹³, and omalizumab, an anti-IgE antibody, was an effective adjunct in patients with persistent symptoms in the Turkish series ⁹⁹. A trial of treatment is therefore a much lower-stakes decision than a diagnostic label, which is one reason the label dispute has not been resolved by outcomes.

What the test misses, and what falsely raises it

Food anaphylaxis is the most important blind spot and has been known to be one since at least 2006, when George Caughey wrote that mature beta-tryptase may fail to increase in food anaphylaxis ²³. The 2012 emergency department series put numbers to it: tryptase was higher in drug-triggered than in food-triggered reactions both acutely (p = 0.045) and at baseline (p = 0.019), and overall it did not rise at all in 36.3 percent of patients with clinical anaphylaxis ²⁵. Nobody has established why. The leading explanations are that gastrointestinal mast cells and basophils contribute mediators other than tryptase, that the reaction is less hemodynamically severe on average, and that absorption from the gut gives a slower, lower peak. All three are plausible; none is proven.

Timing defeats the test in both directions. Drawn in the first 15 to 30 minutes it may not have risen; drawn the following morning it has largely decayed, with a half-life of about 2 hours ¹². A baseline sample taken too soon after the reaction will still be elevated, which can make a real rise look like no rise at all, and a single acute value without any baseline is close to uninterpretable given the wide population range ⁹.

After death, the number means something else. Post-mortem tryptase in femoral blood is elevated by processes that have nothing to do with allergy, and the clinical cutoff of 11.4 micrograms per liter is unusable. A five-year retrospective study comparing 9 anaphylactic deaths with 45 controls found an optimal cutoff of 53.8 micrograms per liter, with sensitivity 89 percent and specificity 93 percent, and no significant contribution from age, sex, post-mortem interval or resuscitation ⁴⁵. A review of the same question notes that there is still no international consensus reference range for post-mortem tryptase and that interpretation is confounded by putrefaction and by the sampling site ¹⁰⁰.

Renal failure raises the baseline. A 2026 retrospective review of 96 nephrology outpatients, excluding anyone with mastocytosis, the hereditary trait or a transplant, found median baseline tryptase rising across chronic kidney disease stages from 3.3 ng/mL at stage 1 to 11.1 ng/mL at stage 4, a significant difference across stages (p = 0.02) ³⁰. This matters practically: a dialysis patient who reacts during a session may have a baseline near the diagnostic threshold before anything happens, and a 2026 case report of anaphylaxis to a polysulfone dialyzer made exactly that point, using a basophil activation test instead because tryptase was uninterpretable ¹⁰¹.

Myeloid neoplasms raise it without any allergic disease at all, as above ^29,53, and so, slightly, do helminth infections and end-stage kidney disease in the same large series ²⁹. Age raises it steadily ⁹, and women and heavy drinkers run lower ⁹.

Finally, a normal tryptase can accompany a very severe reaction through a mechanism that does not involve mast cell granules at all. Platelet-activating factor was raised in patients with anaphylaxis at 805 plus or minus 595 picograms per milliliter against 127 plus or minus 104 in controls, correlated with severity, and the enzyme that inactivates it was lowest in nine patients who died of peanut anaphylaxis ¹⁰². In 2026 a retrospective review of 778 patients assessed for multisystem reactions to insect stings found that use of lipid-lowering medication, which lowers the carrier of that inactivating enzyme, was associated with severe anaphylaxis at an adjusted odds ratio of 2.0 (95 percent confidence interval 1.3 to 3.1, p = 0.0036); in a sensitivity analysis substituting baseline tryptase for mastocytosis in 197 patients the association was directionally consistent but not significant ^102,103. Severity has more than one axis, and tryptase measures only one of them.

Tryptase in asthma, and the drugs aimed at it

The airway was the first place tryptase was looked for as a disease mechanism rather than a marker. In 1988 Sally Wenzel, Alpha Fowler and Lawrence Schwartz measured it in bronchoalveolar lavage fluid before and after segmental allergen challenge in four groups. At baseline, tryptase was significantly higher in atopic asthmatics than in any other group; after challenge it rose in atopic asthmatics from 2.0 plus or minus 1.7 to 10.1 plus or minus 8.2 ng/mL, and in atopic non-asthmatics only from 0.5 to 1.4 ng/mL, while non-atopic subjects did not change at all ⁴³. Mast cells in the asthmatic airway are both more loaded and more readily triggered.

The first therapeutic test came in 2001. APC 366, an inhaled selective tryptase inhibitor, was given to 16 mild atopic asthmatics in a randomized, double-blinded crossover trial, three times daily for four days before allergen challenge. It significantly reduced the late asthmatic response, both the area under the curve (p = 0.012) and the maximum fall in forced expiratory volume (p = 0.007), had no significant effect on the early response or on bronchial hyperresponsiveness ⁴⁷. That is a positive result on a physiological surrogate in 16 people over four days, which is a long way from a treatment, and the compound did not progress.

The modern attempt used the structure against itself. In 2019 a team at Genentech reported that tryptase was elevated in severe asthma independent of type 2 inflammatory biomarker status, that the count of active beta-tryptase alleles correlated with blood tryptase levels, and that asthma patients carrying more active alleles derived less benefit from anti-IgE treatment ³⁷. They then engineered an antibody that does not compete for the blocked active site but destabilizes the interfaces that hold the ring together, dissociating active tetramers into inactive monomers; a 2.15-angstrom crystal structure of the complex showed how ³⁷. In a humanized mouse the antibody blocked IgE-mediated systemic anaphylaxis, and in Ascaris-sensitized cynomolgus monkeys it inhibited airway tryptase ³⁷. Every author on that paper with a Genentech affiliation had a commercial interest in the molecule, which is disclosed in the affiliations and is not a criticism of the data.

The clinical program then failed, and failed informatively. A phase 1 study in 106 healthy participants, 82 of whom received the antibody MTPS9579A, found it well tolerated with no serious or severe adverse events and demonstrated dose-dependent reduction of active tryptase in nasal lining fluid ³¹. Modeling from those data predicted that 1800 mg intravenously every four weeks would suppress 95.7 percent of active tryptase at steady-state trough ⁴¹. That dose was taken into a phase 2a trial of 134 patients with uncontrolled asthma for 48 weeks, and it missed its primary endpoint, time to first composite exacerbation, with a hazard ratio of 0.90 (95 percent confidence interval 0.55 to 1.47, p = 0.6835) ⁴².

The companion phase 1c study explains why, and is the most useful part of the program. In 27 patients, concentrations of the antibody in bronchial lining fluid were 6.8-fold lower than in the nose, while bronchial active and total tryptase were 119-fold and 30-fold higher there respectively; remodeling on the real airway numbers predicted that 3800 mg every four weeks would be needed to achieve 95 percent inhibition ⁴². The exacerbation rate in the placebo group was also low, which limits what any trial of that size could have shown ⁴². The honest summary is that the hypothesis was not tested: the drug did not reach the compartment where the enzyme is, at a dose that could have engaged it. A 2026 review in Pharmacological Reviews surveys mast cell proteases and their inhibitors as candidate therapies and places both chymase and tryptase inhibitors in the same position, biologically attractive and clinically unproven ³².

What else is being measured, 2023 to 2026

The search for something better than tryptase is driven by its negative predictive value, which is 44 to 53 percent in the two validation series ^14,59. A 2019 review set out the candidates and the criteria an ideal marker would need to meet, namely a usable half-life, undemanding sample handling and affordable assay: platelet-activating factor, chymase, carboxypeptidase A3, dipeptidyl peptidase I, basogranulin and the chemokine CCL-2 ¹⁰⁰. None has entered routine practice in the seven years since.

Platelet-activating factor has the strongest outcome data and the worst practicality. In 41 patients with anaphylaxis against 23 controls, serum levels were 805 plus or minus 595 against 127 plus or minus 104 picograms per milliliter, the proportion with raised levels increased stepwise from 20 percent in grade 1 to 100 percent in grade 3 reactions, and the activity of the enzyme that inactivates it was significantly lower in nine patients who died of peanut anaphylaxis than in any control group ¹⁰². It is unstable in the tube and no clinical assay is widely available, which is why a drug-interaction study was the route by which the finding reached practice: in 778 patients assessed for insect-sting reactions, lipid-lowering medication, which reduces the lipoprotein carrier of that inactivating enzyme, was associated with severe anaphylaxis at an adjusted odds ratio of 2.0 (95 percent confidence interval 1.3 to 3.1, p = 0.0036), an association from a retrospective chart review across three countries ¹⁰³.

Cell-based assays are the growth area. The basophil activation test, which measures the appearance of CD63 and CD203c on a patient's own basophils after exposure to a suspected trigger in the tube, has moved from research into selected clinical use for food allergy and for perioperative and drug hypersensitivity, where it can distinguish IgE-mediated reactions from cytokine release and can identify a culprit when skin testing is equivocal ¹⁰⁴. Mast cell activation tests, in which a patient's serum is used to sensitize cultured mast cells, are being developed alongside it ¹⁰⁴. A 2026 review of perioperative hypersensitivity places these tests in a stepwise sequence with skin testing and, where necessary, provocation, rather than as a replacement for tryptase ¹⁰⁴.

In Hymenoptera venom allergy, a 2026 review lists the biomarkers under study beyond tryptase and KIT: osteopontin, prostaglandin D2 metabolites, regulatory T cell signatures and multi-omic profiles, and concludes that no single test predicts severity, so a multimodal individualized strategy remains necessary ¹⁰⁵. In the mast cell itself, MRGPRX2, a receptor that triggers degranulation without IgE in response to drugs, neuropeptides and other cationic compounds, has become the main mechanistic candidate for reactions that do not fit the allergic model, and its expression was raised in gut mast cells of people with hereditary alpha-tryptasemia and inflammatory bowel disease in a 2026 study ^90,106. And in animal work, transepidermal water loss, the rate at which water evaporates through the skin, rose reproducibly during both passive and active murine food anaphylaxis and tracked reaction severity, offering a real-time non-invasive measure that a blood test cannot give ¹⁰⁷.

Two cautions about this literature. First, almost all of it is association: a marker that is higher in severe reactions is not thereby a cause of them, and no candidate has been tested prospectively against clinical decisions. Second, the field is asking a test to do two different jobs, confirm that an event was mast-cell-mediated and predict who will react severely in future, and a marker can be good at one and useless at the other.

What was believed, and is not

That the tryptase circulating at baseline is alpha-tryptase. This was the explicit conclusion of the 1995 paper that introduced the two-antibody assay, and the title said so ³⁶. By 2006 the correction was in print: people lacking alpha genes entirely have near-normal circulating tryptase, so the baseline pool cannot be mainly alpha; it is pro-beta-tryptase, the inactive precursor, secreted constitutively by resting mast cells ^2,23.

That alpha-tryptase is a functionless relic. The 2002 crystal structure showing a blocked substrate-binding region made this the standard view for seventeen years ⁷. It ended in 2019 with the demonstration that alpha and beta protomers assemble into natural heterotetramers with a substrate repertoire neither homotetramer has, activating protease-activated receptor 2 and cleaving the EMR2 mechanosensor ²⁰.

That an elevated baseline tryptase means mast cell disease. For two decades a baseline above 20 ng/mL pointed first at mastocytosis. Since 2016 the commonest explanation has been a common inherited copy-number variant present in about one person in twenty ^18,19,61, which one 2025 review estimates accounts for up to 72 percent of elevations ⁸⁶, and since 2023 the threshold itself has been individualized by genotype, so that a level above 100 ng/mL can be normal for a particular person and a level of 12 can be abnormal for another ^69,88.

That hereditary alpha-tryptasemia causes a multisystem syndrome. The 2016 discovery paper linked the trait to irritable bowel symptoms, cutaneous complaints, connective tissue abnormalities and dysautonomia ¹⁸. When carriers were identified in a random population rather than through a symptom-driven referral, there was no difference in symptoms, medical history or urinary mast cell mediators against controls, and the raised tryptase was the only reproducible feature ⁶³; a British referral series found no dose-response between copy number and symptoms, and asymptomatic relatives with the same genotype ¹⁹. The association with severe anaphylaxis, by contrast, has replicated across independent cohorts and remains ^61,62,87.

That a normal tryptase excludes anaphylaxis. It never did, but the point had to be measured before it was accepted: tryptase does not rise in roughly a third of clinical anaphylaxis presenting to an emergency department, and the negative predictive value of the consensus formula is 44 to 53 percent even in the controlled setting of the operating room ^14,25,59.

That the clinical post-mortem cutoff applies after death. It does not. The optimal femoral post-mortem threshold in one five-year series was 53.8 micrograms per liter, nearly five times the clinical value, and there is still no internationally agreed reference range ^45,100.

That inhibiting tryptase would treat asthma. A small physiological trial in 2001 was encouraging ⁴⁷ and a well-designed antibody program followed ³⁷, but the phase 2a trial missed its primary endpoint, and the companion airway study showed the dose tested could not have inhibited bronchial tryptase in the first place ⁴². The hypothesis is not refuted; it is untested at an adequate dose, which is a different and more honest statement.

That the WHO tryptase criterion is sufficient to find clonal disease. In 374 venom-allergic patients with normal baseline tryptase, sensitive blood testing found KIT D816V in 8 percent, rising to 18.2 percent of those with the most severe reactions ²⁶, and in a mastocytosis series 26 of 27 patients with a baseline below 20 ng/mL were mutation positive in blood ²⁷. The threshold misses clonal disease that a cheap blood mutation test finds.

What is still unknown

Why food anaphylaxis so often fails to raise tryptase. The observation is forty years old and robust ^23,25, and the explanations on offer, basophil involvement, gut mast cell phenotype, slower absorption kinetics, have not been tested against one another in people.

What tryptase actually does during a human anaphylactic reaction. Protease-activated receptor 2 activation and endothelial permeability are demonstrated in vitro and in cell systems ^35,61, the heterotetramer effects on EMR2 are demonstrated biochemically and in cultured mast cells ²⁰, and the humanized mouse shows that blocking the enzyme reduces IgE-mediated anaphylaxis ³⁷. Whether the enzyme is a driver of the human reaction or mostly a bystander marker of it has never been separated in a human trial, because no adequately dosed inhibitor has reached one.

Why the same copy-number variant produces debilitating symptoms in some carriers and nothing in others, including within the same family ^19,63. Modifier genes, mast cell number, co-inherited atopy and ascertainment bias are all candidates. A 2025 survey of 69 patients with the trait who had undergone extensive additional genetic testing found mostly normal results and no clustering that would suggest a common co-inherited disorder ¹⁰⁸.

Whether the trait should be treated at all, and with what. No randomized trial of any treatment exists in hereditary alpha-tryptasemia; current recommendations rest on expert opinion, observational series and case reports, and consist of the same antihistamines, mast cell stabilizers and, in some cases, omalizumab used for clonal disease ^92,109. The 2026 finding that carriers respond less well to omalizumab in severe allergic asthma complicates even that ⁸⁹.

Where the diagnostic threshold should sit now that it is personal. Copy-number-adjusted reference values exist ⁶⁹, a correction factor for the mastocytosis criteria has been proposed ⁸⁸, and the WHO figure of 20 ng/mL remains in the formal criteria ^16,17,66. These have not been reconciled, and no prospective study has shown that genotype-adjusted thresholds change outcomes rather than just reclassifying people.

How prevalent mast cell activation syndrome is. The two published estimates differ by orders of magnitude and neither comes from a study designed to answer the question ^60,72,77. A population-based study with prespecified criteria, blinded assessment and complete tryptase sampling would settle it and has not been done, which the 2026 World Allergy Organization survey names as a priority ⁷⁶.

Whether treating the underlying clone prevents anaphylaxis in mastocytosis. The PIONEER data are the only randomized evidence and the event numbers, 4 of 141 on avapritinib against 3 of 71 on placebo, cannot support a conclusion in either direction ³⁹.

What the gut findings mean. Mast cell numbers and MRGPRX2 expression are higher in the intestines of carriers with inflammatory bowel disease and in celiac patients with persistent symptoms ^90,91, and gastrointestinal complaints are what most carriers present with ⁹². Whether that is cause, consequence or coincidence is open, and the studies are small, cross-sectional and unblinded.

Where it connects

Sources

109 sources, numbered as they are cited. Every one was checked against PubMed or its publisher before it was cited here; the note under each says what it shows and what it does not.

1. 1
   Schwartz LB, Lewis RA, Austen KF. Tryptase from human pulmonary mast cells. Purification and characterization.J Biol Chem · 1981 · 256(22):11939-43PMID 7028744

   The purification. Gives the tetramer structure, the subunit masses of 37,000 and 35,000 in equal molar ratio, the holoenzyme mass of about 144,000, and the content of 6 to 19 micrograms per million mast cells. No DOI is listed in the PubMed record.

2. 2
   Vitte J. Human mast cell tryptase in biology and medicine.Mol Immunol · 2015 · 63(1):18-24doi:10.1016/j.molimm.2014.04.001 · PMID 24793463

   A review. Useful for the distinction between the continuously secreted immature monomer that makes the baseline and the mature tetramer released on degranulation.

3. 3
   Pallaoro M, Fejzo MS, Shayesteh L, Blount JL, Caughey GH. Characterization of genes encoding known and novel human mast cell tryptases on chromosome 16p13.3.J Biol Chem · 1999 · 274(6):3355-62doi:10.1074/jbc.274.6.3355 · PMID 9920877

   Maps the tryptase genes to 16p13.3 and works out which sequences are alleles at which locus. The naming in this paper predates TPSAB1 and TPSB2.

4. 4
   Caughey GH, Raymond WW, Blount JL, et al. Characterization of human gamma-tryptases, novel members of the chromosome 16p mast cell tryptase and prostasin gene families.J Immunol · 2000 · 164(12):6566-75doi:10.4049/jimmunol.164.12.6566 · PMID 10843716

   Adds gamma-tryptase, a membrane-anchored relative, and the pseudogenes to the locus map. Gamma-tryptase is not measured by clinical assays.

5. 5
   Schwartz LB, Bradford TR. Regulation of tryptase from human lung mast cells by heparin. Stabilization of the active tetramer.J Biol Chem · 1986 · 261(16):7372-9PMID 3519608

   Shows that heparin holds the tetramer together and that inactivation is dissociation into monomers, not degradation. Source of the 6-to-8-minute half-life of activity without heparin. No DOI in the record.

6. 6
   Pereira PJ, Bergner A, Macedo-Ribeiro S, et al. Human beta-tryptase is a ring-like tetramer with active sites facing a central pore.Nature · 1998 · 392(6673):306-11doi:10.1038/32703 · PMID 9521329

   The 3-angstrom crystal structure. Explains the resistance to endogenous inhibitors and the heparin requirement, and is the structural basis for the later antibody that dissociates the tetramer.

7. 7
   Marquardt U, Zettl F, Huber R, Bode W, Sommerhoff C. The crystal structure of human alpha1-tryptase reveals a blocked substrate-binding region.J Mol Biol · 2002 · 321(3):491-502doi:10.1016/s0022-2836(02)00625-3 · PMID 12162961

   Explains why alpha homotetramers are not productive proteases. The authors note that activity could in principle be generated by an induced fit, which anticipates the 2019 heterotetramer finding.

8. 8
   Soto D, Malmsten C, Blount JL, Muilenburg DJ, Caughey GH. Genetic deficiency of human mast cell alpha-tryptase.Clin Exp Allergy · 2002 · 32(7):1000-6doi:10.1046/j.1365-2222.2002.01416.x · PMID 12100045

   Genotyping of 274 individuals. Source of the 29 percent overall and 45 percent white alpha-deficiency figures and the alpha allele frequency of 0.23. Ethnic comparisons are from convenience samples, not a population survey.

9. 9
   Gonzalez-Quintela A, Vizcaino L, Gude F, et al. Factors influencing serum total tryptase concentrations in a general adult population.Clin Chem Lab Med · 2010 · 48(5):701-6doi:10.1515/CCLM.2010.124 · PMID 20178448

   A random sample of 420 adults from one Spanish municipality: median 5.1 micrograms per liter, range under 1 to 30.7, continuous rise with age, lower in women and heavy drinkers, no independent effect of atopy. Single-population cross-sectional study.

10. 10
    Valent P, Hoermann G, Bonadonna P, et al. The Normal Range of Baseline Tryptase Should Be 1 to 15 ng/mL and Covers Healthy Individuals With HαT.J Allergy Clin Immunol Pract · 2023 · 11(10):3010-3020doi:10.1016/j.jaip.2023.08.008 · PMID 37572755

    Expert proposal from the European Competence Network on Mastocytosis and the American Initiative in Mast Cell Diseases, after their 2022 meeting: define the normal range in asymptomatic people, carriers of the trait included, as 1 to 15 ng/mL, to avoid overinterpretation, unnecessary referral and anxiety. A consensus derived from a literature screen, not a new population study.

11. 11
    Beyens M, Toscano A, Ebo D, Gülen T, Sabato V. Diagnostic Significance of Tryptase for Suspected Mast Cell Disorders.Diagnostics (Basel) · 2023 · 13(24):3662doi:10.3390/diagnostics13243662 · PMID 38132246

    A practical review. Source of the sampling windows (acute within 4 hours, baseline at least 24 hours after the event), of the statement that 11.4 ng/mL is the manufacturer's upper limit of normal and has been debated, and of the list of other causes of a raised level, including chronic kidney disease, obesity and hematological neoplasms.

12. 12
    Schwartz LB, Yunginger JW, Miller J, Bokhari R, Dull D. Time course of appearance and disappearance of human mast cell tryptase in the circulation after anaphylaxis.J Clin Invest · 1989 · 83(5):1551-5doi:10.1172/JCI114051 · PMID 2468689

    The kinetic study behind the sampling window: peak at 1 to 2 hours in three experimentally stung subjects, half-life about 2 hours, possible non-detection in the first 15 to 30 minutes, and sample stability data. Three subjects plus two emergency presentations; the half-life is well replicated since.

13. 13
    Valent P, Akin C, Arock M, et al. Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal.Int Arch Allergy Immunol · 2012 · 157(3):215-25doi:10.1159/000328760 · PMID 22041891

    The consensus document from the 2010 working conference, source of the three-criterion definition and of the requirement for a substantial transient rise in tryptase. A consensus statement; the arithmetic threshold within it was not derived from a validation cohort.

14. 14
    Baretto RL, Beck S, Heslegrave J, et al. Validation of international consensus equation for acute serum total tryptase in mast cell activation: A perioperative perspective.Allergy · 2017 · 72(12):2031-2034doi:10.1111/all.13226 · PMID 28609557

    Eighty-two patients investigated after suspected anaphylaxis under general anesthesia, 60 meeting World Allergy Organization criteria. Source of sensitivity 78 percent, specificity 91 percent, positive predictive value 98 percent, negative predictive value 44 percent, and the median 1.34-hour time to peak. A selected perioperative population with known timing, which flatters sensitivity relative to community practice.

15. 15
    Valent P, Bonadonna P, Hartmann K, et al. Why the 20% + 2 Tryptase Formula Is a Diagnostic Gold Standard for Severe Systemic Mast Cell Activation and Mast Cell Activation Syndrome.Int Arch Allergy Immunol · 2019 · 180(1):44-51doi:10.1159/000501079 · PMID 31256161

    The consensus group's own restatement and defense of the formula, which it dates to its 2012 proposal. Argues that baseline tryptase varies with disease and genetic background, so each rise must be judged against the person's own baseline, and states that independent groups have validated it. A position paper by the formula's authors, not new data.

16. 16
    Valent P, Akin C, Hartmann K, et al. Updated Diagnostic Criteria and Classification of Mast Cell Disorders: A Consensus Proposal.Hemasphere · 2021 · 5(11):e646doi:10.1097/HS9.0000000000000646 · PMID 34901755

    Retains a baseline above 20 ng/mL as a minor criterion for systemic mastocytosis while stating explicitly that hereditary alpha-tryptasemia and various myeloid neoplasms also cause elevations; adds CD30 as a minor criterion and defines bone marrow mastocytosis. A consensus document from a working conference.

17. 17
    Khoury JD, Solary E, Abla O, et al. The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Myeloid and Histiocytic/Dendritic Neoplasms.Leukemia · 2022 · 36(7):1703-1719doi:10.1038/s41375-022-01613-1 · PMID 35732831

    The current World Health Organization classification, within which mastocytosis and its diagnostic criteria sit. Cited for the classification framework, not for data.

18. 18
    Lyons JJ, Yu X, Hughes JD, et al. Elevated basal serum tryptase identifies a multisystem disorder associated with increased TPSAB1 copy number.Nat Genet · 2016 · 48(12):1564-1569doi:10.1038/ng.3696 · PMID 27749843

    The discovery of hereditary alpha-tryptasemia: duplications and triplications at TPSAB1 segregating with high tryptase in 35 families, with a gene-dose effect, confirmed in 172 further individuals. The multisystem symptom list in the title and abstract came from symptomatic families and was not reproduced in later unselected populations.

19. 19
    Robey RC, Wilcock A, Bonin H, et al. Hereditary Alpha-Tryptasemia: UK Prevalence and Variability in Disease Expression.J Allergy Clin Immunol Pract · 2020 · 8(10):3549-3556doi:10.1016/j.jaip.2020.05.057 · PMID 32553831

    Five percent prevalence in an unselected British birth cohort of 432, all carriers having a baseline of 8 ng/mL or above, plus a referral series of 70 with the symptom frequencies quoted. Key negative finding: no greater symptom burden with triplications or quintuplications than duplications, and asymptomatic relatives with the same genotype.

20. 20
    Le QT, Lyons JJ, Naranjo AN, et al. Impact of naturally forming human α/β-tryptase heterotetramers in the pathogenesis of hereditary α-tryptasemia.J Exp Med · 2019 · 216(10):2348-2361doi:10.1084/jem.20190701 · PMID 31337736

    Shows that mixed alpha/beta tetramers form naturally and, unlike either homotetramer, activate protease-activated receptor 2 and cleave the EMR2 mechanosensor. Biochemistry and cell work; it supplies a mechanism for the clinical associations but does not test them in patients.

21. 21
    Khalaf R, Prosty C, Davalan W, et al. Diagnostic Utility of Biomarkers in Anaphylaxis: A Systematic Review and Meta-Analysis.J Allergy Clin Immunol Pract · 2025 · 13(6):1342-1349.e12doi:10.1016/j.jaip.2025.04.008 · PMID 40239922

    Twenty-eight studies published 2004 to 2024, 18,749 patients, 3,329 with anaphylaxis. Pooled tryptase sensitivity 0.49 and specificity 0.82 (24 studies); histamine 0.76 and 0.69; too few data to pool platelet-activating factor, its inactivating enzyme or urinary prostaglandin D2. Pools studies with different definitions and sampling times, which the heterogeneity of the field makes unavoidable.

22. 22
    Schwartz LB, Metcalfe DD, Miller JS, Earl H, Sullivan T. Tryptase levels as an indicator of mast-cell activation in systemic anaphylaxis and mastocytosis.N Engl J Med · 1987 · 316(26):1622-6doi:10.1056/NEJM198706253162603 · PMID 3295549

    The paper that made tryptase a clinical test. Small numbers: 17 patients with mastocytosis, 6 with anaphylaxis, 20 controls. Establishes that the level is raised in mast cell events and not in myocardial disease or sepsis; does not address sensitivity in unselected anaphylaxis.

23. 23
    Caughey GH. Tryptase genetics and anaphylaxis.J Allergy Clin Immunol · 2006 · 117(6):1411-4doi:10.1016/j.jaci.2006.02.026 · PMID 16751005

    The correction of the 1995 attribution: baseline tryptase is mainly constitutively secreted pro-beta-tryptase, not alpha. Also states plainly that mature tryptase may fail to rise in food anaphylaxis and may rise non-specifically after death. A review, not new data.

24. 24
    Svetina M, Lyons JJ, Kopač P, et al. Tryptase Locus Variation Contributes to Normal-Range Basal Serum Tryptase Variability and Is Associated With Anaphylaxis.Clin Exp Allergy · 2026 · online ahead of printdoi:10.1111/cea.70448 · PMID 42844895

    464 people with venom allergy or sensitization, excluding KIT D816V and the hereditary trait. Active tryptase allele number correlated with baseline level (r = 0.34), and four active beta alleles were associated with less anaphylaxis than two or three (26.7 versus 42.3 percent, p = 0.024). An association within one referral population; the mechanism is not established.

25. 25
    Sala-Cunill A, Cardona V, Labrador-Horrillo M, et al. Usefulness and limitations of sequential serum tryptase for the diagnosis of anaphylaxis in 102 patients.Int Arch Allergy Immunol · 2012 · 160(2):192-9doi:10.1159/000339749 · PMID 23018683

    Prospective emergency department study with samples at 1 to 2, 4 to 6 and 12 to 24 hours and at baseline. Source of the finding that tryptase was not raised in 36.3 percent, and unchanged from baseline in 60.6 percent of those. The strongest single demonstration of the test's poor sensitivity outside the operating room.

26. 26
    Šelb J, Rijavec M, Eržen R, et al. Routine KIT p.D816V screening identifies clonal mast cell disease in patients with Hymenoptera allergy regularly missed using baseline tryptase levels alone.J Allergy Clin Immunol · 2021 · 148(2):621-626.e7doi:10.1016/j.jaci.2021.02.043 · PMID 33753098

    Prospective screening of 374 venom-allergic patients. KIT D816V in 8 percent of the 351 with a normal baseline tryptase, concentrated in grade IV reactions (18.2 percent), odds ratio 10.25 for severe anaphylaxis. Also shows that hereditary alpha-tryptasemia accounted for 15 of 23 elevated baselines, and the two causes together for 20 of 23.

27. 27
    Kristensen T, Vestergaard H, Bindslev-Jensen C, Møller MB, Broesby-Olsen S. Sensitive KIT D816V mutation analysis of blood as a diagnostic test in mastocytosis.Am J Hematol · 2014 · 89(5):493-8doi:10.1002/ajh.23672 · PMID 24443360

    Detection in peripheral blood in 94 percent of 83 adults with systemic mastocytosis, 100 percent specific against clinically relevant controls, and positive in 26 of 27 patients whose tryptase was below 20 ng/mL. A single-center case series with its own controls, not a prospective screening study.

28. 28
    Sucre-Adrianza I, Caligaris H, Morales-Cabeza C, et al. The REMA Score Revisited: An Optimized Algorithm for Early Prediction of Clonal Mast Cell Disease.Allergy · 2026 · 81(8):2792-2803doi:10.1111/all.70379 · PMID 42156185

    Retrospective revalidation in 1,204 patients with severe mast cell mediator symptoms and no skin lesions referred to the Spanish Network on Mastocytosis. Score sensitivity 87 to 90 percent, specificity 34 to 35 percent; blood KIT D816V detected in only 29 percent of clonal cases; in low scorers a raised tryptase without hereditary alpha-tryptasemia had an odds ratio of 5.42; a refined algorithm reached 57 percent specificity at 86 percent sensitivity. A referral population.

29. 29
    Sperr WR, El-Samahi A, Kundi M, et al. Elevated tryptase levels selectively cluster in myeloid neoplasms: a novel diagnostic approach and screen marker in clinical haematology.Eur J Clin Invest · 2009 · 39(10):914-23doi:10.1111/j.1365-2362.2009.02184.x · PMID 19522836

    914 patients with hematological malignancies plus 402 others. Source of the healthy median of 5.2 ng/mL and of the proportions above 15 ng/mL in acute myeloid leukemia, chronic myeloid leukemia and myelodysplastic syndrome, and of the note that end-stage kidney disease and helminth infection raise it slightly.

30. 30
    Gansert E, Estrada-Mendizabal RJ, Voelker DH, et al. Serum baseline tryptase levels across chronic kidney disease stages: A retrospective report.J Allergy Clin Immunol Glob · 2026 · 5(6):100777doi:10.1016/j.jacig.2026.100777 · PMID 42729308

    Ninety-six nephrology outpatients with mastocytosis, the hereditary trait and transplant recipients excluded. Median baseline tryptase rose from 3.3 ng/mL at stage 1 to 11.1 at stage 4 (p = 0.02). Small, retrospective, single health system, and no stage 5 median is reported.

31. 31
    Rymut SM, Sukumaran S, Sperinde G, et al. Dose-dependent inactivation of airway tryptase with a novel dissociating anti-tryptase antibody (MTPS9579A) in healthy participants: A randomized trial.Clin Transl Sci · 2022 · 15(2):451-463doi:10.1111/cts.13163 · PMID 34581002

    Phase 1 in 106 healthy participants, 82 on active drug: safe, with dose-dependent reduction of active tryptase in nasal lining fluid. Healthy volunteers only; nasal fluid turned out not to predict the bronchial compartment.

32. 32
    Derakhshani A, Mahajan L, Lesack K, et al. Mast cell proteases and their significance in physiology, pathology, and therapeutic approaches.Pharmacol Rev · 2026 · 78(4):100144doi:10.1016/j.pharmr.2026.100144 · PMID 42361439

    A current review of mast cell proteases and of protease inhibitors as candidate therapies. One author is affiliated with Genentech, which developed the anti-tryptase antibody.

33. 33
    GLENNER GG, COHEN LA. Histochemical demonstration of a species-specific trypsin-like enzyme in mast cells.Nature · 1960 · 185:846-7doi:10.1038/185846a0 · PMID 13828452

    The first demonstration of a trypsin-like enzyme in mast cells. The PubMed record carries no abstract, so it is cited for the existence and date of the observation, not for a number.

34. 34
    Fukuoka Y, Schwartz LB. Human beta-tryptase: detection and characterization of the active monomer and prevention of tetramer reconstitution by protease inhibitors.Biochemistry · 2004 · 43(33):10757-64doi:10.1021/bi049486c · PMID 15311937

    Shows the monomer is not simply inert: active at pH 6 with a polyanion, and inhibitable by ordinary protease inhibitors that cannot touch the tetramer. In vitro biochemistry; the in vivo relevance at inflamed, acidic tissue sites is proposed rather than shown.

35. 35
    Molino M, Barnathan ES, Numerof R, et al. Interactions of mast cell tryptase with thrombin receptors and PAR-2.J Biol Chem · 1997 · 272(7):4043-9doi:10.1074/jbc.272.7.4043 · PMID 9020112

    Cell-culture work showing tryptase activates protease-activated receptor 2 with a half-maximal effect at 1 nanomolar, and does not cleave thrombin receptors on platelets. In vitro only.

36. 36
    Schwartz LB, Sakai K, Bradford TR, Ren S, Zweiman B, Worobec AS, Metcalfe DD. The alpha form of human tryptase is the predominant type present in blood at baseline in normal subjects and is elevated in those with systemic mastocytosis.J Clin Invest · 1995 · 96(6):2702-10doi:10.1172/JCI118337 · PMID 8675637

    Introduces the B12 and G5 capture assays and the total-to-mature ratio. Its central claim, that the baseline form is alpha-tryptase, was later corrected; the assay framework and the ratio it describes remain valid.

37. 37
    Maun HR, Jackman JK, Choy DF, et al. An Allosteric Anti-tryptase Antibody for the Treatment of Mast Cell-Mediated Severe Asthma.Cell · 2019 · 179(2):417-431.e19doi:10.1016/j.cell.2019.09.009 · PMID 31585081

    The antibody that dissociates the tetramer, with a 2.15-angstrom structure of the complex, plus the observations that active beta-allele count correlates with blood tryptase and that patients with more active alleles respond less well to anti-IgE. Preclinical: humanized mice and Ascaris-sensitized monkeys. Most authors were employees of the manufacturer, Genentech.

38. 38
    Gülen T, Akin C, Bonadonna P, et al. Selecting the Right Criteria and Proper Classification to Diagnose Mast Cell Activation Syndromes: A Critical Review.J Allergy Clin Immunol Pract · 2021 · 9(11):3918-3928doi:10.1016/j.jaip.2021.06.011 · PMID 34166845

    The consensus authors' direct response to the competing criteria, arguing that the alternatives lack specificity and validation and that misdiagnosis delays recognition of other conditions. A position review by one side of the dispute.

39. 39
    Pongdee T, Castells M, Akin C, et al. Anaphylaxis events in the PIONEER study of avapritinib in indolent systemic mastocytosis.World Allergy Organ J · 2026 · 19(4):101352doi:10.1016/j.waojou.2026.101352 · PMID 41867266

    The only randomized data on whether KIT-directed therapy prevents anaphylaxis: 4 of 141 on avapritinib and 3 of 71 on placebo over 24 weeks. The authors state that larger studies with longer follow-up are required; the event numbers cannot support any conclusion. Industry-sponsored.

40. 40
    Hartmann K, Alvarez-Twose I, Bernstein JA, et al. Prevalence of KIT D816V in anaphylaxis or systemic mast cell activation.J Allergy Clin Immunol · 2026 · 157(2):409-418doi:10.1016/j.jaci.2025.10.010 · PMID 41399928

    The PROSPECTOR trial: 381 patients selected for moderate to severe sting anaphylaxis, a documented 20 percent plus 2 rise, or multisystem reactions with a baseline of 8 ng/mL or more. KIT D816V in blood in 15 (4 percent), 12 of them with a baseline below 20 ng/mL; clonal disease in 29 (8 percent); hereditary alpha-tryptasemia in 36 percent. Three authors were employees of Blueprint Medicines, which makes a KIT D816V inhibitor. Published online in October 2025.

41. 41
    Rymut SM, Henderson LM, Poon V, et al. A mechanistic PK/PD model to enable dose selection of the potent anti-tryptase antibody (MTPS9579A) in patients with moderate-to-severe asthma.Clin Transl Sci · 2023 · 16(4):694-703doi:10.1111/cts.13483 · PMID 36755366

    The pharmacokinetic and pharmacodynamic model that predicted 95.7 percent suppression of active airway tryptase at 1800 mg every four weeks. The prediction rested on estimated airway tryptase levels and drug partitioning, both of which the later phase 1c measurements contradicted. Authors were employees of the manufacturer.

42. 42
    Rhee H, Henderson LM, Bauer RN, et al. Airway tryptase levels inform the lack of clinical efficacy of the tryptase inhibitor MTPS9579A in asthma.Allergy · 2024 · 79(11):2993-3004doi:10.1111/all.16309 · PMID 39250147

    The negative phase 2a trial, 134 patients over 48 weeks, hazard ratio 0.90 (0.55-1.47, p = 0.6835), reported together with the phase 1c airway measurements that explain it: 6.8-fold lower drug and 119-fold higher active tryptase in bronchial than nasal fluid, with 3800 mg every four weeks predicted as the dose actually needed. Manufacturer-run and manufacturer-reported; the frank publication of the dosing failure is to its credit.

43. 43
    Wenzel SE, Fowler AA, Schwartz LB. Activation of pulmonary mast cells by bronchoalveolar allergen challenge. In vivo release of histamine and tryptase in atopic subjects with and without asthma.Am Rev Respir Dis · 1988 · 137(5):1002-8doi:10.1164/ajrccm/137.5.1002 · PMID 2461667

    Airway tryptase before and after segmental allergen challenge in four small groups (n = 3 to 7 each). Shows higher baseline and a larger rise in atopic asthmatics. Too small to quantify an effect size reliably.

44. 44
    Yunginger JW, Nelson DR, Squillace DL, et al. Laboratory investigation of deaths due to anaphylaxis.J Forensic Sci · 1991 · 36(3):857-65PMID 1856650

    The first postmortem tryptase series: raised in 17 of 19 anaphylaxis deaths (9 of 9 sting, 6 of 8 food, 2 of 2 diagnostic agents) in serum taken before or within 24 hours after death, and below 10 ng/mL in all 57 postmortem samples from six control deaths. Small, and the clean control result was not reproduced later. No DOI in the record.

45. 45
    Tse R, Wong CX, Kesha K, et al. Post mortem tryptase cut-off level for anaphylactic death.Forensic Sci Int · 2018 · 284:5-8doi:10.1016/j.forsciint.2017.12.035 · PMID 29331682

    Nine anaphylactic deaths against 45 controls, giving an optimal femoral post-mortem cutoff of 53.8 micrograms per liter at 89 percent sensitivity and 93 percent specificity. Very small numbers for a receiver-operating-characteristic cutoff; it should be read as an order-of-magnitude correction to the clinical threshold, not a precise value.

46. 46
    Cialona R, Tettamanti C, Abbona G, et al. Postmortem tryptase as a diagnostic marker in fatal anaphylaxis: A systematic review and meta-analysis.Leg Med (Tokyo) · 2026 · 85:102911doi:10.1016/j.legalmed.2026.102911 · PMID 42442173

    Seven studies, 105 anaphylactic deaths and 449 controls: postmortem tryptase about 8.7 times higher in anaphylaxis (ratio of means 8.68, 2.12 to 35.57), pooled sensitivity 0.80 and specificity 0.92. Cutoffs varied widely, and the authors warn against reading a universal threshold into them. Substantial heterogeneity.

47. 47
    Krishna MT, Chauhan A, Little L, et al. Inhibition of mast cell tryptase by inhaled APC 366 attenuates allergen-induced late-phase airway obstruction in asthma.J Allergy Clin Immunol · 2001 · 107(6):1039-45doi:10.1067/mai.2001.115631 · PMID 11398082

    Randomized double-blinded crossover trial in 16 mild atopic asthmatics over four days. Positive on the late asthmatic response, negative on hyperresponsiveness and on the early response. A surrogate endpoint in a very small sample; the drug was not developed further.

48. 48
    Valent P, Horny HP, Escribano L, et al. Diagnostic criteria and classification of mastocytosis: a consensus proposal.Leuk Res · 2001 · 25(7):603-25doi:10.1016/s0145-2126(01)00038-8 · PMID 11377686

    The 2001 consensus that defined systemic mastocytosis by major histological criteria and minor cytological and biochemical criteria, the basis of later World Health Organization classifications. Lawrence Schwartz and K Frank Austen are among the authors.

49. 49
    Valent P, Hartmann K, Hoermann G, et al. Harmonization of Diagnostic Criteria in Mastocytosis for Use in Clinical Practice: WHO vs ICC vs AIM/ECNM.J Allergy Clin Immunol Pract · 2024 · 12(12):3250-3260.e5doi:10.1016/j.jaip.2024.08.044 · PMID 39216803

    The European and American expert consensus group compares its criteria with the World Health Organization and International Consensus Classification versions, describes the latter as slightly modified, and proposes harmonizing all three. States that the group's criteria, developed since 2001, served as the basis for the World Health Organization classification over two decades. Written by the group whose criteria are under comparison.

50. 50
    Tremaine WJ, Brzezinski A, Katz JA, et al. Treatment of mildly to moderately active ulcerative colitis with a tryptase inhibitor (APC 2059): an open-label pilot study.Aliment Pharmacol Ther · 2002 · 16(3):407-13doi:10.1046/j.1365-2036.2002.01194.x · PMID 11876693

    Open-label phase 2 pilot: 56 adults given 20 mg subcutaneously twice daily for 28 days; 16 (29 percent) responded and 5 (9 percent) reached complete remission. No placebo group, so the response rate cannot be separated from natural fluctuation or expectation.

51. 51
    Rice KD, Wang VR, Gangloff AR, et al. Dibasic inhibitors of human mast cell tryptase. Part 2: structure-activity relationships and requirements for potent activity.Bioorg Med Chem Lett · 2000 · 10(20):2361-6doi:10.1016/s0960-894x(00)00485-6 · PMID 11055356

    Medicinal chemistry from Axys Pharmaceuticals, all authors company scientists, describing the inhibitor series and stating that APC-2059 had been advanced to phase 2 trials in psoriasis and ulcerative colitis. Cited for the drug's origin and development status, not for clinical data.

52. 52
    Sperr WR, Jordan JH, Fiegl M, et al. Serum tryptase levels in patients with mastocytosis: correlation with mast cell burden and implication for defining the category of disease.Int Arch Allergy Immunol · 2002 · 128(2):136-41doi:10.1159/000059404 · PMID 12065914

    Sixteen cutaneous and 43 systemic mastocytosis patients; correlation of r = 0.8 between serum level and marrow infiltration. Also records the exception that all three patients with isolated bone marrow mastocytosis had levels below 20 ng/mL.

53. 53
    Klion AD, Noel P, Akin C, et al. Elevated serum tryptase levels identify a subset of patients with a myeloproliferative variant of idiopathic hypereosinophilic syndrome associated with tissue fibrosis, poor prognosis, and imatinib responsiveness.Blood · 2003 · 101(12):4660-6doi:10.1182/blood-2003-01-0006 · PMID 12676775

    Fifteen patients, 9 with elevated tryptase. Small, but the association with the FIP1L1-PDGFRA fusion and with imatinib response has held. An example of tryptase as a hematology marker rather than an allergy one.

54. 54
    Garcia-Montero AC, Jara-Acevedo M, Teodosio C, et al. KIT mutation in mast cells and other bone marrow hematopoietic cell lineages in systemic mast cell disorders: a prospective study of the Spanish Network on Mastocytosis (REMA) in a series of 113 patients.Blood · 2006 · 108(7):2366-72doi:10.1182/blood-2006-04-015545 · PMID 16741248

    Source of the 93 percent figure for KIT D816V in indolent and aggressive systemic mastocytosis, and of the much lower 29 percent in the well-differentiated variant. Sorted cell populations, prospective.

55. 55
    Akin C, Valent P, Metcalfe DD. Mast cell activation syndrome: proposed diagnostic criteria.J Allergy Clin Immunol · 2010 · 126(6):1099-104.e4doi:10.1016/j.jaci.2010.08.035 · PMID 21035176

    The first formal proposal of criteria. An expert proposal explicitly offered as a basis for further study and validation, not a validated instrument.

56. 56
    Sargur R, Cowley D, Murng S, et al. Raised tryptase without anaphylaxis or mastocytosis: heterophilic antibody interference in the serum tryptase assay.Clin Exp Immunol · 2011 · 163(3):339-45doi:10.1111/j.1365-2249.2010.04287.x · PMID 21303361

    Eighty-three rheumatoid-factor-positive samples tested before and after heterophile blocking tubes: 14 fell by more than 17 percent and 8 of those 14 returned to normal. Shows that a false-positive result can be an assay artifact; a selected set of samples, so it does not give the frequency in ordinary practice.

57. 57
    Schliemann S, Seyfarth F, Hipler UC, Elsner P. Impact of age and heterophilic interference on the basal serum tryptase, a risk indication for anaphylaxis, in 1,092 dermatology patients.Acta Derm Venereol · 2012 · 92(5):484-9doi:10.2340/00015555-1245 · PMID 22170044

    Retrospective analysis of 1,092 dermatology patients without mastocytosis: tryptase rose with age, and of 106 raised samples retested after heterophile blocking only one fell by more than half. The unselected counterweight to the 2011 series.

58. 58
    Lyons JJ, Sun G, Stone KD, et al. Mendelian inheritance of elevated serum tryptase associated with atopy and connective tissue abnormalities.J Allergy Clin Immunol · 2014 · 133(5):1471-4doi:10.1016/j.jaci.2013.11.039 · PMID 24472624

    A letter with no abstract in the PubMed record; cited for the existence and date of the observation that high tryptase can be inherited as a dominant trait, two years before the gene was found.

59. 59
    Vitte J, Amadei L, Gouitaa M, et al. Paired acute-baseline serum tryptase levels in perioperative anaphylaxis: An observational study.Allergy · 2019 · 74(6):1157-1165doi:10.1111/all.13752 · PMID 30793322

    Retrospective study of 102 perioperative patients comparing four algorithms. The 2012 consensus equation performed best: 75 percent sensitivity, 86 percent specificity, 94 percent positive and 53 percent negative predictive value. Also shows mature tryptase adds little, particularly below an acute total of 16 micrograms per liter.

60. 60
    Afrin LB, Ackerley MB, Bluestein LS, et al. Diagnosis of mast cell activation syndrome: a global "consensus-2".Diagnosis (Berl) · 2020 · 8(2):137-152doi:10.1515/dx-2020-0005 · PMID 32324159

    The competing criteria. Argues that the earlier consensus underdiagnoses, estimates prevalence at up to 17 percent of the general population, and concludes that either proposal is valid pending better research. The prevalence figure is an inference from referral experience, not a population measurement.

61. 61
    Lyons JJ, Chovanec J, O'Connell MP, et al. Heritable risk for severe anaphylaxis associated with increased α-tryptase-encoding germline copy number at TPSAB1.J Allergy Clin Immunol · 2021 · 147(2):622-632doi:10.1016/j.jaci.2020.06.035 · PMID 32717252

    Prevalence of 5.6 percent in 125 healthy volunteers and 5.3 percent in 398 non-atopic controls; relative risk 2.0 for grade IV venom anaphylaxis, 17 percent in idiopathic anaphylaxis, 12.2 percent in systemic mastocytosis, and relative risk 9.5 for systemic anaphylaxis within mastocytosis. The endothelial permeability experiments are in vitro. Cohorts were drawn from referral centers, so the anaphylaxis groups are selected.

62. 62
    Greiner G, Sprinzl B, Górska A, et al. Hereditary α tryptasemia is a valid genetic biomarker for severe mediator-related symptoms in mastocytosis.Blood · 2021 · 137(2):238-247doi:10.1182/blood.2020006157 · PMID 32777817

    Independent replication in 180 mastocytosis patients against 180 controls, with a separate validation cohort of 61. Trait present in 17.2 percent versus 4.4 percent; tryptase higher in carriers (median 49.6 versus 34.5 ng/mL) independent of mast cell burden; venom hypersensitivity and severe cardiovascular reactions more frequent.

63. 63
    Chollet MB, Akin C. Hereditary alpha tryptasemia is not associated with specific clinical phenotypes.J Allergy Clin Immunol · 2022 · 149(2):728-735.e2doi:10.1016/j.jaci.2021.06.017 · PMID 34174297

    The reversal. Trait found in 7.5 percent of a random biorepository population and 18 percent of mastocytosis patients, with no difference in symptoms, medical history or urinary mast cell mediators between carriers and controls. Elevated baseline tryptase was the only consistent marker. Cross-sectional, with clinician interview and examination.

64. 64
    Koch D, Wortmann F, Recke A, et al. Extended multisystem manifestations of hereditary α-tryptasemia in an allergy center cohort.J Allergy Clin Immunol Glob · 2026 · 5(4):100737doi:10.1016/j.jacig.2026.100737 · PMID 42292655

    Prospective enrollment of 332 allergy patients with a baseline of 8 ng/mL or more at one German center; questionnaire in 256. Carriers of the trait reported a heavier symptom load (9.3 against 6.5 points), including fatigue, concentration problems and orthostatic dysregulation. Self-report in a referral population; the counter-evidence to the 2022 no-phenotype finding.

65. 65
    Mateja A, Wang Q, Chovanec J, et al. Defining baseline variability of serum tryptase levels improves accuracy in identifying anaphylaxis.J Allergy Clin Immunol · 2022 · 149(3):1010-1017.e10doi:10.1016/j.jaci.2021.08.007 · PMID 34425177

    Models ordinary baseline variability in 93 people and tests in validation cohorts. Source of the false-positive rates for the 20 percent plus 2 rule (9.7 percent overall, 18 percent in hereditary alpha-tryptasemia, 30 percent in indolent systemic mastocytosis) and of the proposed acute-to-baseline ratio of 1.685. The anaphylaxis test set was only 22 patients.

66. 66
    Arber DA, Orazi A, Hasserjian RP, et al. International Consensus Classification of Myeloid Neoplasms and Acute Leukemias: integrating morphologic, clinical, and genomic data.Blood · 2022 · 140(11):1200-1228doi:10.1182/blood.2022015850 · PMID 35767897

    The parallel classification published the same year. Cited to show that two competing hematology classifications exist and that both retain the tryptase threshold within the mastocytosis criteria.

67. 67
    Pardanani A. Systemic mastocytosis in adults: 2023 update on diagnosis, risk stratification and management.Am J Hematol · 2023 · 98(7):1097-1116doi:10.1002/ajh.26962 · PMID 37309222

    A hematology review. Cited for the current statement of the criteria: a major criterion of multifocal mast cell clusters, and minor criteria including raised serum tryptase, CD25, CD2 or CD30 expression and activating KIT mutations.

68. 68
    Buttgereit T, Gu S, Carneiro-Leão L, et al. Idiopathic mast cell activation syndrome is more often suspected than diagnosed-A prospective real-life study.Allergy · 2022 · 77(9):2794-2802doi:10.1111/all.15304 · PMID 35364617

    Prospective 12-week study of 100 people with suspected mast cell activation syndrome in Berlin: 53 percent suspected it from self-evaluation, 2 of 79 sampled after an episode met the 20 percent plus 2 rise, and the syndrome was confirmed in 2 percent. Single center; the senior author co-wrote the consensus authors' 2021 critical review.

69. 69
    Chovanec J, Tunc I, Hughes J, et al. Genetically defined individual reference ranges for tryptase limit unnecessary procedures and unmask myeloid neoplasms.Blood Adv · 2023 · 7(9):1796-1810doi:10.1182/bloodadvances.2022007936 · PMID 36170795

    The 2022 copy-number-adjusted threshold work. Explains the mechanism of the elevation as a co-inherited overactive promoter, and derives personal reference values: without the trait, a baseline above 11.4 ng/mL frequently identifies indolent clonal disease; with it, levels above 100 ng/mL can be normal. Modeling from referral cohorts; prospective outcome data are not yet available.

70. 70
    Schuler CF, O'Shea KM, Troost JP, et al. Transepidermal water loss rises before food anaphylaxis and predicts food challenge outcomes.J Clin Invest · 2023 · 133(16)doi:10.1172/JCI168965 · PMID 37402149

    Two hundred nine oral food challenges conducted and adjudicated by staff blinded to the readings. Skin water loss rose 48 minutes before clinically evident anaphylaxis, and continuous monitoring gave 96 percent specificity 38 minutes ahead. A single center; the human work the later mouse studies were modeled on.

71. 71
    Golden DBK, Wang J, Waserman S, et al. Anaphylaxis: A 2023 practice parameter update.Ann Allergy Asthma Immunol · 2024 · 132(2):124-176doi:10.1016/j.anai.2023.09.015 · PMID 38108678

    The current United States practice parameter. States that serum tryptase is important for diagnosing anaphylaxis and for identifying underlying mast cell disorders, and that evaluation for mastocytosis, including bone marrow biopsy, should be considered in adults with severe sting anaphylaxis or recurrent idiopathic anaphylaxis. Published online in December 2023.

72. 72
    Zaghmout T, Maclachlan L, Bedi N, Gülen T. Low Prevalence of Idiopathic Mast Cell Activation Syndrome Among 703 Patients With Suspected Mast Cell Disorders.J Allergy Clin Immunol Pract · 2024 · 12(3):753-761doi:10.1016/j.jaip.2023.11.041 · PMID 38056692

    The best available estimate of how often the consensus criteria are met: 31 of 703 consecutive referrals, 4.4 percent, after full allergy work-up, KIT D816V analysis and marrow examination where indicated. Retrospective, single center, and it measures the referred population, not the general one.

73. 73
    Farley M, Estrada-Mendizabal RJ, Gansert EA, et al. Prevalence of mast cell activation disorders and hereditary alpha tryptasemia among patients with postural orthostatic tachycardia syndrome and Ehlers-Danlos syndrome: A systematic review.Ann Allergy Asthma Immunol · 2025 · 135(1):97-102doi:10.1016/j.anai.2025.03.022 · PMID 40185471

    Systematic review that found no study meeting its prespecified diagnostic criteria linking mast cell activation disorders or hereditary alpha-tryptasemia to postural orthostatic tachycardia syndrome or Ehlers-Danlos syndrome; one study came close. Absence of evidence, which the authors say calls for research with strict criteria rather than settling the question.

74. 74
    Lyons JJ. Appraisal of the evidence linking hereditary α-tryptasemia with mast cell disorders, hypermobility and dysautonomia.Allergy Asthma Proc · 2025 · 46(1):4-10doi:10.2500/aap.2025.46.240088 · PMID 39741374

    A review by the scientist who described the trait. States that more recent studies have shown some previously held associations with congenital hypermobility and postural orthostatic tachycardia syndrome to be lacking, and describes the trait as a common modifier of mast cell-mediated reactions.

75. 75
    Korošec P, Lyons JJ, Svetina M, et al. Hereditary α-tryptasemia is Associated With Anaphylaxis to Antibiotics and Monoclonal Antibodies.J Allergy Clin Immunol Pract · 2025 · 13(6):1449-1456.e4doi:10.1016/j.jaip.2025.04.013 · PMID 40239920

    Prospective Slovenian discovery cohort of 99 and Czech validation cohort of 26 patients with drug anaphylaxis. Trait in 13 and 15 percent; present in every patient with a raised baseline (11.6 to 21.9 ng/mL, 14 people); more frequent after antibiotics or monoclonal antibodies (26 against 7 percent, odds ratio 4.1, 1.3 to 11.1). Small, with a wide interval.

76. 76
    Giavina-Bianchi P, Giavina-Bianchi M, Morais-Almeida M, et al. Mast cell activation syndrome: Global perspectives from a World Allergy Organization survey on knowledge, diagnosis, and access to care.World Allergy Organ J · 2026 · 19(10):101470doi:10.1016/j.waojou.2026.101470 · PMID 42857128

    Cross-sectional international survey of allergists and clinical immunologists. Documents the gap between suspected and confirmed cases everywhere, names tryptase dynamics and urinary metabolites as the main bottleneck, and concludes that structural limitations and diagnostic overextension coexist. A survey of clinicians' reports, not of patients.

77. 77
    Afrin LB, Blitshteyn S, Bluestein LS, et al. Progress in mast cell activation syndrome: the global consensus-2 diagnostic criteria at six years.Diagnosis (Berl) · 2026 · online ahead of printdoi:10.1515/dx-2026-0016 · PMID 42240520

    The consensus-2 authors' six-year review, arguing that feared overdiagnosis has not materialized while conceding that research remains early and that objective assessment of treatment response is difficult. A position review by one side of the dispute; no new prevalence data.

78. 78
    Aziz Q, Harris LA, Goodman BP, Simrén M, Shin A. AGA Clinical Practice Update on GI Manifestations and Autonomic or Immune Dysfunction in Hypermobile Ehlers-Danlos Syndrome: Expert Review.Clin Gastroenterol Hepatol · 2025 · 23(8):1291-1302doi:10.1016/j.cgh.2025.02.015 · PMID 40387691

    American Gastroenterological Association expert review. Advises tryptase at baseline and 1 to 4 hours after a symptom flare when mast cell activation syndrome is suspected, and states that universal testing for it in hypermobility disorders is not supported. Expert opinion without formal evidence grading.

79. 79
    Shaker MS, Wallace DV, Golden DBK, et al. Anaphylaxis-a 2020 practice parameter update, systematic review, and Grading of Recommendations, Assessment, Development and Evaluation (GRADE) analysis.J Allergy Clin Immunol · 2020 · 145(4):1082-1123doi:10.1016/j.jaci.2020.01.017 · PMID 32001253

    The United States practice parameter. Cited for the position that anaphylaxis is a clinical diagnosis treated first with epinephrine; it does not make treatment contingent on any laboratory result.

80. 80
    Sampson HA, Mendelson L, Rosen JP. Fatal and near-fatal anaphylactic reactions to food in children and adolescents.N Engl J Med · 1992 · 327(6):380-4doi:10.1056/NEJM199208063270603 · PMID 1294076

    Thirteen children and adolescents, six of whom died. Cited for the timing of epinephrine: the six who died had symptoms within 3 to 30 minutes and only two received epinephrine in the first hour, while all survivors but one received it within 30 minutes. A case series, not a controlled comparison.

81. 81
    Lin RY, Schwartz LB, Curry A, et al. Histamine and tryptase levels in patients with acute allergic reactions: An emergency department-based study.J Allergy Clin Immunol · 2000 · 106(1 Pt 1):65-71doi:10.1067/mai.2000.107600 · PMID 10887307

    Ninety-seven adults sampled prospectively in an emergency department: histamine above 10 nanomoles per liter in 42 but total tryptase above 15 ng/mL in only 20, which the authors read as basophil involvement in many reactions. Uses fixed cutoffs rather than paired baselines, which was standard at the time.

82. 82
    Valent P, Akin C, Bonadonna P, et al. Proposed Diagnostic Algorithm for Patients with Suspected Mast Cell Activation Syndrome.J Allergy Clin Immunol Pract · 2019 · 7(4):1125-1133.e1doi:10.1016/j.jaip.2019.01.006 · PMID 30737190

    The 2019 refinement: an explicit sequence that establishes systemic mast cell activation, then looks for severe allergy or mastocytosis, before any syndrome label. The authors state that it requires validation, which has not been published.

83. 83
    De Amici M, Taietti I, Castagnoli R, et al. Understanding Tryptase Physiology, Clinical Significance, and Diagnostic Applications: Where Do We Stand?Biomolecules · 2026 · 16(9):1360doi:10.3390/biom16091360 · PMID 42793192

    A 2026 narrative review of the whole subject. Useful as a statement of the current consensus position: the 20 percent plus 2 formula validated, hereditary alpha-tryptasemia recognized as a common cause of elevated baselines, and interpretation dependent on knowing both baseline and genotype.

84. 84
    Bonadonna P, Perbellini O, Passalacqua G, et al. Clonal mast cell disorders in patients with systemic reactions to Hymenoptera stings and increased serum tryptase levels.J Allergy Clin Immunol · 2009 · 123(3):680-6doi:10.1016/j.jaci.2008.11.018 · PMID 19135713

    Of 379 patients with systemic sting reactions, 44 (11.6 percent) had tryptase above 11.4 ng/mL; of 34 who had marrow examined, 21 had indolent systemic mastocytosis and 9 monoclonal mast cell activation syndrome. Only those with raised tryptase were biopsied, so the denominator for clonal disease in venom allergy overall is not established here.

85. 85
    Pornsuthirat P, Owattanapanich W, Wongsa C, Thongngarm T, Sompornrattanaphan M. Clonal Mast Cell Disorders and Mutation Profile in Adults Initially Presenting with Mast Cell Activation (Anaphylaxis) versus Non-Anaphylactic Presentations: A Joint Allergy-Hematology Cohort.J Asthma Allergy · 2026 · 19:594281doi:10.2147/JAA.S594281 · PMID 42004892

    Twenty-four clinician-selected adults taken to marrow and 66-gene sequencing at a Thai center. Clonal disease in 1 of 14 presenting with anaphylaxis against 10 of 10 with non-allergic presentations; median baseline tryptase 22.4 against 3.2 ng/mL. Small and selected by clinician judgment, which the authors state.

86. 86
    Tüsüz Önata E, Özdemir Ö, Savaşan S. Hereditary alpha tryptasemia and clinical implications.World J Clin Cases · 2025 · 13(21):104723doi:10.12998/wjcc.v13.i21.104723 · PMID 40726930

    A review; source of the estimate that the trait accounts for up to 72 percent of elevated baseline tryptase. The figure is drawn from published cohorts rather than an original measurement.

87. 87
    Lang A, Kubala S, Grieco MC, et al. Severe food allergy reactions are associated with α-tryptase.J Allergy Clin Immunol · 2023 · 152(4):933-939doi:10.1016/j.jaci.2023.07.014 · PMID 37558059

    Two cohorts totaling 119 subjects. Presence of alpha-tryptase associated with more food-triggered anaphylaxis (p = 0.026) and higher severity scores (p = 0.003); the difference in severe reactions during oral food challenge, 20 of 31 versus 1 of 6, did not reach significance (p = 0.066). Small, and the challenge cohort is selected.

88. 88
    McMurray JC, Schornack BJ, Villar J, George TI, Boggs NA. Utility of tryptase genotyping in the screening, diagnosis, and management of systemic mastocytosis.Front Allergy · 2025 · 6:1599358doi:10.3389/falgy.2025.1599358 · PMID 40497258

    Explains how the copy-number-adjusted reference ranges are applied to the World Health Organization criteria, including the correction factor for the bone marrow mastocytosis cutoff of 125 ng/mL and the B-finding of 200 ng/mL. A review of practice, not a validation study.

89. 89
    Rijavec M, Svetina M, Škrgat S, et al. Hereditary α-tryptasemia is associated with response to omalizumab in severe allergic asthma.Ann Allergy Asthma Immunol · 2026 · online ahead of printdoi:10.1016/j.anai.2026.10.014 · PMID 42880632

    181 patients across Slovenian and British centers. The trait was found in 20 percent of poor responders to omalizumab against 5 percent of responders, odds ratio 4.6 (1.5-12.3), holding at 4.56 after adjustment. Also records that 4 of 15 carriers had a baseline tryptase below 8 ng/mL, so the usual screening threshold missed them. Retrospective and from two referral centers.

90. 90
    Galeas-Pena M, Lyons JJ, Llivichuzhca-Loja D, et al. MRGPRX2-expressing mast cells are increased in the GI tract of individuals with active inflammatory bowel disease and hereditary α-tryptasemia.Front Allergy · 2026 · 6:1726096doi:10.3389/falgy.2025.1726096 · PMID 41647192

    Genotyping of 854 biobanked inflammatory bowel disease samples with spatial transcriptomics on 4 versus 4 and mass cytometry on 5 versus 9. Increased gut mast cells and increased MRGPRX2 and SIGLEC8 expression in carriers. Very small comparison groups; mechanistic and hypothesis-generating.

91. 91
    Therrien A, Akula S, Galeas-Pena M, et al. Hereditary Alpha-Tryptasemia Is Associated With Ongoing Symptoms in Individuals With Celiac Disease Despite Following a Gluten-free Diet.Am J Gastroenterol · 2026 · 121(2):517-525doi:10.14309/ajg.0000000000003537 · PMID 40367491

    Prospective cohort of 153. Trait prevalence in celiac disease was no higher than the general population at 6.4 percent, but all 9 carriers had ongoing symptoms, and duodenal mast cell counts were 27.3 per high-power field against 22.0 and 18.4. Small numbers; association only.

92. 92
    Vainer D, Peterson K. Non allergic gastrointestinal manifestations of hereditary alpha-tryptasemia.Front Allergy · 2025 · 6:1598309doi:10.3389/falgy.2025.1598309 · PMID 40556656

    Review of the gastrointestinal presentation. States explicitly that there are no randomized controlled trials of therapy for these symptoms and that current treatment rests on expert opinion, observational studies and case reports.

93. 93
    Weiss M, Rossignol J, Campeotto F, et al. Characteristics and outcomes of patients with pediatric-onset non-mastocytosis mast cell activation disorders: A CEREMAST study.Pediatr Allergy Immunol · 2026 · 37(5):e70373doi:10.1111/pai.70373 · PMID 42149735

    Forty-four children from the French national referral center: only 8 met full criteria for idiopathic mast cell activation syndrome, 36 fell into a not-otherwise-specified category, and the trait was present in 5 of 33 tested (15.2 percent). Antihistamines with or without a leukotriene antagonist markedly reduced symptoms, uncontrolled.

94. 94
    Tockova O, Planinsek Rucigaj T, Ivancan S, et al. Hereditary α-Tryptasemia and Peripheral Blood KIT D816V Mutation in Patients with Pediatric Mastocytosis.Int J Mol Sci · 2025 · 26(13):6023doi:10.3390/ijms26136023 · PMID 40649802

    Prospective cohort of 68 children with cutaneous mastocytosis: 83.8 percent carried at least one alpha-tryptase gene but none had the trait, and 7 of 68 (10.3 percent) were KIT D816V positive in blood. Shows the adult picture does not transfer to children; single referral center.

95. 95
    Hamilton MJ, Hornick JL, Akin C, Castells MC, Greenberger NJ. Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations.J Allergy Clin Immunol · 2011 · 128(1):147-152.e2doi:10.1016/j.jaci.2011.04.037 · PMID 21621255

    Eighteen prospectively evaluated patients. Describes the clinical picture and a 67 percent response rate to mediator-targeting drugs; uncontrolled, single center, and the entry criteria were symptom-based.

96. 96
    Valent P, Akin C, Bonadonna P, et al. Mast cell activation syndrome: importance of consensus criteria and call for research.J Allergy Clin Immunol · 2018 · 142(3):1008-1010doi:10.1016/j.jaci.2018.06.004 · PMID 29928922

    A letter from the consensus authors; no abstract in the record. Cited for the existence and date of the position that specific criteria should be retained.

97. 97
    Weiler CR, Austen KF, Akin C, et al. AAAAI Mast Cell Disorders Committee Work Group Report: Mast cell activation syndrome (MCAS) diagnosis and management.J Allergy Clin Immunol · 2019 · 144(4):883-896doi:10.1016/j.jaci.2019.08.023 · PMID 31476322

    A professional society work group report stating explicitly that its criteria are intended to diagnose most cases without overdiagnosing people who have other conditions. Expert recommendation, not evidence.

98. 98
    Theoharides TC, Kempuraj D, Maitland A. Mast cell activation disorders: mechanisms, comorbidities and look-alike.Expert Rev Clin Immunol · 2026 · 22(7):767-787doi:10.1080/1744666X.2026.2699311 · PMID 42405823

    A review making the mechanistic objection to a tryptase-anchored definition: mediator release can occur by several routes without tryptase being released. An opinion-led review from authors who favor broader recognition of these disorders.

99. 99
    Katran ZY, Argın Ö, Erdem S, Bulut İ. Mast cell activation syndromes in clinical practice: diagnostic challenges, phenotypes, and real-life management.Postepy Dermatol Alergol · 2026 · 43(4):391-395doi:10.5114/ada.2026.162040 · PMID 42890065

    Twenty-one adults with non-clonal mast cell activation syndromes seen over a decade at one Istanbul center. All documented the 20 percent plus 2 rise during follow-up; only 6 were classified as idiopathic after comorbidities were accounted for. Very small and retrospective, but it is one of the few series to apply the criterion prospectively over time.

100. 100
     Beck SC, Wilding T, Buka RJ, Baretto RL, Huissoon AP, Krishna MT. Biomarkers in Human Anaphylaxis: A Critical Appraisal of Current Evidence and Perspectives.Front Immunol · 2019 · 10:494doi:10.3389/fimmu.2019.00494 · PMID 31024519

     Review of candidate biomarkers beyond tryptase and of the post-mortem problem. States that there is no international consensus reference range for post-mortem tryptase. A narrative review, not a systematic one.

101. 101
     Jung JY, Moon DH, Kim H, et al. Anaphylaxis during hemodialysis associated with a polysulfone membrane: evidence from basophil activation testing.Kidney Res Clin Pract · 2026 · online ahead of printdoi:10.23876/j.krcp.26.013 · PMID 42299450

     A single case report with review. Cited only for the clinical point that serum tryptase is of limited diagnostic use in advanced chronic kidney disease because the baseline is chronically raised, and that a basophil activation test can be used instead. One patient.

102. 102
     Vadas P, Gold M, Perelman B, et al. Platelet-activating factor, PAF acetylhydrolase, and severe anaphylaxis.N Engl J Med · 2008 · 358(1):28-35doi:10.1056/NEJMoa070030 · PMID 18172172

     Forty-one patients with anaphylaxis and 23 controls, plus nine fatal peanut cases. Establishes the correlation of platelet-activating factor with severity and the inverse correlation with its inactivating enzyme. Case-control and retrospective in part; causation is inferred, not demonstrated.

103. 103
     Sohng K, Lee E, Golden D, et al. Lipid-Lowering Medications Increase the Severity of Hymenoptera Venom Anaphylaxis.J Allergy Clin Immunol Pract · 2026 · online ahead of printdoi:10.1016/j.jaip.2026.08.027 · PMID 42665188

     Retrospective chart review of 778 patients in three countries: lipid-lowering medication associated with severe anaphylaxis at an adjusted odds ratio of 2.0 (1.3-3.1). The mechanism, interference with platelet-activating factor inactivation, is the authors' rationale rather than something the study measured, and the tryptase sensitivity analysis in 197 patients was not significant.

104. 104
     Ebo DG, Peeters L, Toscano A, et al. Under the Drapes: Unmasking the Mechanisms and Clinical Diagnosis of Perioperative Hypersensitivity.Curr Allergy Asthma Rep · 2026 · 26(1)doi:10.1007/s11882-026-01296-z · PMID 42821016

     Review of the stepwise diagnostic approach to perioperative reactions, placing basophil and mast cell activation tests alongside tryptase, skin testing and, in selected cases, provocation. Expert review drawing on the authors' own practice.

105. 105
     Wilińska W, Starosz A, Grubczak K. Diagnostics and monitoring in Hymenoptera venom allergy: current and future perspectives.Front Allergy · 2026 · 7:1757776doi:10.3389/falgy.2026.1757776 · PMID 42109509

     Review of current and emerging tests in venom allergy. Source of the list of candidate biomarkers under study, including osteopontin, prostaglandin D2 metabolites, regulatory T cell signatures and multi-omic profiles, and of the statement that normal tryptase values do not exclude severe reactions.

106. 106
     Wu K, Liu J. The MRGPRX2 paradigm shift: Redefining mast cell activation pathways in chronic urticaria.Allergol Select · 2026 · 10:52-62doi:10.5414/ALX02618E · PMID 42058742

     Review of MRGPRX2, the receptor through which drugs, neuropeptides and other cationic compounds trigger mast cells without IgE. Cited for the mechanism, which is relevant to reactions that occur on first exposure and may not follow the allergic pattern.

107. 107
     Woerner BN, Abbo J, Wang A, et al. Transepidermal water loss increases during murine food anaphylaxis and reflects reaction severity.Front Immunol · 2025 · 16:1667569doi:10.3389/fimmu.2025.1667569 · PMID 41112256

     Mouse work. Transepidermal water loss rose reproducibly in passive and active systemic anaphylaxis models and tracked severity, offering a real-time non-invasive readout. Animal evidence; the human observation it is modeled on comes from oral food challenges.

108. 108
     Butterfield JH, Bhasin AK, Ishmael LL, Squire JD. Hereditary Alpha Tryptasemia: Survey of Concomitant Genetic Testing.Int Arch Allergy Immunol · 2025 · 186(11):1057-1064doi:10.1159/000544704 · PMID 39965556

     Records review of 69 patients with the trait: genetic testing had been performed in 73 percent, often extensively, and was mostly normal with no clustering. Evidence against a common co-inherited explanation for the variable phenotype; retrospective and from one center.

109. 109
     Rüfer A, Müllner G, Fuchs O, Sperr WR, Hoermann G. Hereditary alpha-tryptasemia - a potential cause of severe anaphylactic reactions and a modifier of mast cell diseases.Swiss Med Wkly · 2025 · 155:3679doi:10.57187/s.3679 · PMID 40450750

     A review setting out current practice: screen for both KIT D816V and the trait by droplet digital polymerase chain reaction after measuring baseline tryptase, and treat symptomatically. States plainly that no targeted therapy for the trait exists.