If at least 1 major and 1 one minor, or at least 3 minor criteria, are met, the diagnosis of Systemic Mastocytosis (SM) can be established.

Major Criteria: Multifocal dense infiltrates of mast cells in bone marrow or other extracutaneous organ(s) (>15 mast cells in aggregate)

Minor Criteria:

a)      Mast cells in bone marrow or other extracutaneous organ(s) show an abnormal morphology (> 25%)

b)      C-kit mutation at codon 816 in extracutaneous organ(s). (Activating mutations at codon 816; in most cases, c-kit D816V)

c)      Mast cells in bone marrow express CD2 and/or CD25

d)      Serum total tryptase > 20 ng/mL (does not count in patients who have associated hematologic clonal non-mast cell lineage disease-type disease)