What are the consensus criteria for MCAS, and where does the controversy lie?

The ECNM-AIM framework requires three criteria to be met together. Broader definitions exist, but their status and validation differ.

10 sources
6 min read
Clinical review
Verified 9 November 2026

Key points

The ECNM-AIM framework requires three elements at the same time: severe, recurrent systemic episodes involving at least two organ systems; biochemical evidence of mast cell activation; and a response to treatments that target the mediators or their action ^{[1, 2, 3]}.
The preferred blood marker is an acute rise in tryptase of at least 20% above the individual baseline value, plus 2 ng/mL (formula 1.2 × baseline + 2) ^{[4, 3]}.
Response to anti-mediator treatment is only one of the three criteria: on its own, it is not enough to confirm MCAS ^{[1, 3]}.
A much broader approach, known as “consensus-2,” is advocated by its authors in a 2026 review; it is disputed and must not be presented as a consensus adopted by professional societies ^{[5, 3]}.
An international World Allergy Organization survey published in 2026 found marked heterogeneity in practice and a large gap between suspected cases and cases meeting all the criteria ^[6].

The ECNM-AIM framework: three criteria that must all be met

Classification of the forms

Tryptase: what “20% + 2” does and does not mean

Why broader definitions are debated

Differential diagnoses and safety

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.

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, Hartmann K, Bonadonna P, Niedoszytko M, Triggiani M, Arock M, Brockow K. Mast Cell Activation Syndromes: Collegium Internationale Allergologicum Update 2022. Int Arch Allergy Immunol, 183(7):693–705 2022. DOI: 10.1159/000524532. PMID: 35605594.(guideline or consensus)
Limitations: Expert synthesis (Collegium Internationale Allergologicum), not a meta-analysis. Read: full text (PMC9393812).
Declared conflicts of interest: Several authors declare consulting activities, fees or research funding (including Novartis, Blueprint, Deciphera, Thermo Fisher); P. Valent funded by the Austrian Science Fund (FWF)
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
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
Afrin LB, Blitshteyn S, Bluestein LS, Dempsey TT, Maxwell AJ, Miller CS, Nagy È, Nugent DJ, Schofield JR, Weinstock LB, Xi SC, Molderings GJ. Progress in mast cell activation syndrome: the global consensus-2 diagnostic criteria at six years. Diagnosis (Berl) 2026. DOI: 10.1515/dx-2026-0016. PMID: 42240520.(expert opinion)
Limitations: Review written by authors who promote the "consensus-2" framework; it is not a professional society guideline. Read: abstract (full text not consulted).
Declared conflicts of interest: Not reviewed in the part of the source that was read
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, 19(10):101470 2026. DOI: 10.1016/j.waojou.2026.101470. PMID: 42857128.(observational study)
Limitations: Self-reported cross-sectional survey (547 allergists/immunologists analyzed, responses collected March to May 2025); possible response bias; describes respondents' practices, not the prevalence of MCAS. Read: full text (PMC13651491).
Declared conflicts of interest: The authors declare no financial conflicts of interest; funding: not applicable
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
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
Akin C, Gülen T, Castells MC, Oude Elberink H, Valent P. Diagnosis and Management of Patients With Mast Cell Activation Syndromes: Status 2026. J Allergy Clin Immunol Pract, 14(1):19–28 2026. DOI: 10.1016/j.jaip.2025.10.046. PMID: 41285202.(expert opinion)
Limitations: Expert clinical review, not an original study. Read: abstract.
Declared conflicts of interest: Not reviewed in the part of the source that was read
Weiler CR. Mast Cell Activation Syndrome: Tools for Diagnosis and Differential Diagnosis. J Allergy Clin Immunol Pract, 8(2):498–506 2020. DOI: 10.1016/j.jaip.2019.08.022. PMID: 31470118.(evidence synthesis)
Limitations: Narrative clinical review. Read: abstract.
Declared conflicts of interest: Not reviewed in the part of the source that was read

Written by: AI-assisted literature research (ChatGPT) and AI-assisted writing (Claude)
Editor: Jean Viry-Babel
Review status: Clinical review: Dr Françoise Charmoillaux (anesthesiologist)
Approved on: 9 November 2026
Literature search: 8 November 2026
Last verified: 9 November 2026
Geographic scope: international, France, United States
Audience: everyone
Conflicts of interest: No known financial ties. Separately, the publisher is developing a personal approach to these conditions under the name Connected Conditions, which is not cited here (see the legal notice).
Limitations of this page: Presents published criteria intended for medical assessment; it is not a self-diagnosis tool and the page cannot be used to interpret an individual test result. Akin 2026, Afrin 2026 and Weiler 2020 read from their abstract only. Page not reviewed by an allergist or hematologist.