Table 1.

Typical clinical features and symptoms suggesting the presence of systemic mastocytosis (SM)^* or a mast cell activation syndrome

Feature/symptom	Typical laboratory findings
Anaphylaxis with hypotension	Allergy tests (specific IgE) negative
Severe anaphylactic shock after hymenoptera venom exposure**	Allergy tests positive or negative and: tryptase elevated during the event**
Headache plus diarrhea responsive to histamine receptor antagonists	increased histamine levels (plasma, urine), tryptase may or may not increase
Unexplained pruritus (+/- urticaria or flushing) responsive to histamine receptor antagonists	no skin disease, allergy, or internal disorder explaining symptoms are found, tryptase may or may not increase
Other allergy-like symptoms that are responsive to histamine receptor antagonists or mast cell-targeting drugs (like cromolyn)	no allergy and no other disease explaining the symptoms are found, tryptase may or may not increase
Bone pain due to osteopenia or osteoporosis***	T score below -2 (below -2.5) as assessed by age-adjusted osteodensitometry

^*if two or more of these features/symptoms are recorded in the same patient, the likelihood increases that the patient is suffering from SM.

^**meeting the criteria of mast cell activation syndrome (MCAS).

^***counts especially in man, and when other causes of osteoporosis have been excluded.