Criteria for the diagnosis of MCAS:
(1) episodic symptoms consistent with release of mast cell mediators involving 2 or more of the following:
(1a) skin: urticaria, flushing, angioedema
(1b) gastrointestinal tract: nausea, vomiting, diarrhea, abdominal cramping
(1c) cardiovascular system: hypotension, syncope or near syncope, tachycardia
(1d) respiratory: wheezing
(1e) naso-ocular: nasal stuffiness, conjunctival injection, pruritis
(2) partial or complete response to anti-mast cell mediator therapy
(3) presence of urine and/or serum markers of mast cell activation during symptomatic periods that exceed baseline levels
(4) exclusion of other mast cell and idiopathic disorders
Anti-mediator therapy may include:
(1) H1 and H2 histamine receptor inverse agonists (specific antihistamines)
(2) anti-leukotriene drugs (cysteinyl leukotriene receptor blocker, 5-lipoxygenase inhibitor)
(3) mast cell stabilizer such as cromolyn sodium
Rules for marker studies:
(1) If the baseline serum trypase level is > 15 ng/mL, then an increase of serum tryptase concentration on 1 or more symptomatic episodes.
(2) If the baseline serum tryptase level is <= 15 ng/mL, then an increase of serum tryptase concentration on 2 or more symptomatic episodes.
(3) If serum tryptase testing is not available, then less specific assays can be used:
(3a) 24 hour urine histamine metabolite levels
(3b) prostaglandin D2 levels
(3c) prostaglandin D2 metabolite 11-beta-prostaglandin F2.
Other mast cell disorders to exclude:
(1) mastocytosis
(2) monoclonal mast cell activation syndrome
(3) allergic disorder
(4) chronic autoimmune urticaria
(5) physical urticaria
(6) mast cell activation secondary to chronic inflammatory or neoplastic disorders
Other idiopathic disorders to exclude:
(1) anaphylaxis
(2) angioedema
(3) urticaria
