Table 1.

World Health Organization diagnostic criteria for systemic mastocytosis

Major criterion

Multifocal dense infiltrates of MCs (> 15 MCs in aggregates) are detected in sections of BM and/or other extracutaneous organ(s).

Minor criteria

In biopsy sections of BM or other extracutaneous organs, > 25% of the MCs in the infiltrate are spindle shaped; have atypical morphologic features; or, of all MCs in BM aspirate smears, > 25% are immature or atypical.

Detection of an activating point mutation at codon 816 in KIT in BM, blood, or another extracutaneous organ

MCs in BM, blood, or other extracutaneous organs express CD2 and/or CD25 in addition to normal mast cell markers.

Serum total tryptase persistently exceeds 20 ng/mL (unless there is an associated clonal myeloid disorder, in which case this parameter is not valid).

The diagnosis of SM requires at least 1 major criterion and 1 minor criterion or at least 3 minor criteria.