What do tryptase and hereditary alpha-tryptasemia mean?
Acute tryptase, baseline tryptase and hereditary alpha-tryptasemia answer different questions and do not replace a clinical diagnosis.
- 7 sources
- 4 min read
- Clinical review
- Verified 9 November 2026
Key points
- Tryptase is a mediator produced in great abundance by mast cells; an acute rise, compared with the individual baseline value, is the most specific and most reliable marker of systemic mast cell activation under the ECNM-AIM framework [1, 2].
- The “20% + 2” rule refers to an episode-related rise: acute value ≥ 1.2 × baseline value + 2 ng/mL. An isolated high baseline tryptase is neither proof of acute activation nor a diagnosis of MCAS [2, 3].
- Hereditary alpha-tryptasemia (also called hereditary hyper-alpha-tryptasemia, HαT) is an autosomal dominant genetic trait linked to an increased number of copies of the TPSAB1 gene, which encodes alpha-tryptase; it comes with a high-normal (above about 8 ng/mL) or elevated baseline tryptase, but many carriers have no associated symptoms [4, 5].
- HαT is neither mastocytosis nor MCAS; it can nevertheless coexist with these conditions and modify how they present [4, 3].
Acute tryptase and baseline tryptase
In an emergency. If you have trouble breathing, throat swelling or feel faint after an exposure, call 911 (or your local emergency number); never delay emergency care for a blood test.
What is hereditary alpha-tryptasemia?
Tryptase and systemic mastocytosis
What remains uncertain
References and level of evidence
- 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, 157(3):215–225 2012. DOI: 10.1159/000328760. PMID: 22041891.(guideline or consensus)Limitations: Consensus proposal from an expert conference (2010), refined by later updates; not a population study. Read: full text (PMC3224511).Declared conflicts of interest: No declaration found in the text that was read
- 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, 180(1):44–51 2019. DOI: 10.1159/000501079. PMID: 31256161.(evidence synthesis)Limitations: Focused narrative review written by the group that devised the formula; not an original validation study. Read: full text (author manuscript PMC7115850).Declared conflicts of interest: Several authors declare research funding, consulting or fees (including Deciphera, Novartis, Blueprint, Thermo Fisher/Phadia); others declare none
- Lee E, Picard M. Diagnosis and management of mast cell activation syndrome (MCAS) in Canada: a practical approach. Allergy Asthma Clin Immunol, 21(1):49 2025. DOI: 10.1186/s13223-025-00998-9. PMID: 41272881.(evidence synthesis)Limitations: Practical narrative review based on the ECNM-AIM criteria, adapted to the Canadian setting; test availability varies by country. Read: full text (PMC12639879).Declared conflicts of interest: M. Picard: fees from Novartis, Sanofi, Lundbeck and Celltrion unrelated to this work, associate editor of the journal, investigator in a study funded by Telios; E. Lee: none
- Glover SC, Carter MC, Korošec P, Bonadonna P, Schwartz LB, Milner JD, Caughey GH, Metcalfe DD, Lyons JJ. Clinical relevance of inherited genetic differences in human tryptases: Hereditary alpha-tryptasemia and beyond. Ann Allergy Asthma Immunol, 127(6):638–647 2021. DOI: 10.1016/j.anai.2021.08.009. PMID: 34400315.(evidence synthesis)Limitations: Literature review; prevalence estimated mainly in white populations. Read: full text (author manuscript PMC9413800).Declared conflicts of interest: Not reviewed in the part of the source that was read
- von Bubnoff D, Koch D, Stocker H, Ludwig RJ, Wortmann F, von Bubnoff N. The Clinical Features of Hereditary Alpha-Tryptasemia—Implications for Interdisciplinary Practice. Dtsch Arztebl Int, 121(8):258–264 2024. DOI: 10.3238/arztebl.m2023.0287. PMID: 38260947.(evidence synthesis)Limitations: Selective review (selective PubMed search, conference communications and clinical experience); limited prevalence data. Read: full text (PMC11381211).Declared conflicts of interest: The authors declare no conflicts of interest
- 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, 23(8):1291–1302 2025. DOI: 10.1016/j.cgh.2025.02.015. PMID: 40387691.(expert opinion)Limitations: Expert review by the American Gastroenterological Association; without a systematic review, its "Best Practice Advice" statements carry no formal rating of the quality of evidence. Read: detailed abstract.Declared conflicts of interest: Not reviewed in the part of the source that was read
- Valent P, Akin C, Hartmann K, et al. Updated Diagnostic Criteria and Classification of Mast Cell Disorders: A Consensus Proposal. HemaSphere, 5(11):e646 2021. DOI: 10.1097/HS9.0000000000000646. PMID: 34901755.(guideline or consensus)Limitations: Consensus proposal from European and American experts (August 2020 conference); classifications have changed since, and any detailed presentation must state which edition is cited. Read: full text (PMC8659997).Declared conflicts of interest: Several authors declare consulting activities, fees or funding (including Novartis, Deciphera, Blueprint Medicines); the others declare none