Criteria
US/European consensus criteria
A diagnosis of MCAS can be confirmed if the following three criteria are all met:[2][3]
The patient has recurrent acute episodes of symptoms that are typical of mast cell activation and that concurrently affect at least two organ systems.
In many cases, these acute episodes meet the clinical definition of anaphylaxis.
During acute episodes, there is a substantial transient increase in serum tryptase level over the patient’s baseline level.
To fulfil this criterion, serum total tryptase must rise by at least 20% above baseline +2 ng/ml within 4 hours of the onset of a symptomatic episode.
If tryptase testing is unavailable or does not produce a clear result, elevated urinary markers of mast cell activation may be sufficient to meet this criterion.[2][5]
The symptoms show a significant improvement in response to medications that attenuate the production or activity of mast cell-derived mediators. Examples include an antihistamine, H2 antagonist, leukotriene receptor antagonist, or cromolyn.
These criteria are based on those proposed by a US/EU working group that met in 2010 and published their recommendations in 2012 and are sometimes referred to as the “Vienna consensus” criteria.[2] The version summarized here includes a subsequent update to incorporate minor modifications.[5] The criteria have been endorsed by the American Academy of Allergy, Asthma and Immunology.[3]
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