Start

Primary MCAS or CM

End

^* The serum tryptase level may be below the 20 ng/ml threshold, or only transiently elevated.

^** Although an evaluation for systemic mastocytosis generally is recommended in adults with MIS who have no blood count abnormalities or organ dysfunction and a normal or mildly increased serum tryptase level, the value of performing a bone marrow biopsy should be discussed with the patient.

CM, Cutaneous mastocytosis; MC, mast cell; MCAS, mast cell activation syndrome; MIS, mastocytosis in the skin; SM, systemic mastocytosis; PDGFRA, platelet-derived growth factor receptor A; WHO, World Health Organization.

Systemic mastocytosis +/– primary MCAS

In the absence of CM, consider other causes for mast cell activation (e.g., secondary MCAS) (allergies, drugs, infections) or idiopathic MCAS/anaphylaxis

Cutaneous mastocytosis

Evaluation for systemic mastocytosis

Bone marrow biopsy or biopsy of other extracutaneous organ
KIT D816V; if needed, additional KIT gene sequencing
Mast cell immunophenotyping
Screen for FIP1L1-PDGFRA if eosinophilia is present

<3 minor SM criteria fulfilled (KIT D816V⁺ and/or CD25⁺ MC)

KIT wild-type and normal MC morphology/immunophenotype

At least 1 major + 1 minor or 3 minor criteria

WHO criteria for SM not fulfilled but MIS present

Mast cell activation symptoms or anaphylaxis, and/or increased serum tryptase level^* (no MIS, B or C findings, or abnormal blood counts)

Adult-onset MIS^**