Table 4.

Subtypes of mast cell activation syndrome (MCAS) [61,62,63,64].

Subtype of MCAS	Diagnostic Criteria
Primary	Detectable D816 V mutation in C Kit gene, with MC CD25 expresssion, with or without underlying mastocytosis
Secondary	Underlying background, such as allergic diseases, e.g., food allergy, autoimmune diseases, infections, neoplasms
Idiopathic	If both subtypes are excluded

MCAS—mast cell activation syndrome, MC—mast cell, CD—cluster of differentiation.