Table 1.
| Variants of MCAS | Diagnostic Features |
|---|---|
| Primary MCAS (Monoclonal MCAS) |
KIT D816V+; MCs aberrantly express CD25 in most cases, may either fulfill criteria for mastocytosis (SM or CM) or present with only two minor SM criteria. |
| Secondary MCAS | IgE-mediated allergy, another hypersensitivity reaction, or another immunologic disease induces MC activation; no neoplastic MCs or KIT D816V. |
| HαT MCAS | HαT is detected, all diagnostic MCAS criteria are fulfilled, and no related allergic cause or underlying clonal MC disease is detected. |
| Combined MCAS | Patients with MCAS suffering from two or more of the following: (a) CM or SM; (b) overt allergy/atopic disease; (c) a known genetic predisposition such as HαT. |
| Idiopathic MCAS | MCAS criteria are met, but no related reactive disease, no IgE-dependent allergy, and no neoplastic/clonal MCs. |
CM = cutaneous mastocytosis, SM = systemic mastocytosis.