Table 2.

Classification of Mast Cell Activation (MCA) and Related Conditions.

i. According to Organs involved and Severity of Symptoms     Systemic MCA *       Mild or moderate systemic MCA (MCAS criteria not fulfilled)       Severe systemic MCA = MCAS (MCAS criteria fulfilled)     Local MCA (mild/moderate or severe) (MCAS criteria not fulfilled)

ii. According to the Underlying Condition     Primary (clonal) MCA       Cutaneous mastocytosis       Systemic mastocytosis (SM)       1-2 minor SM criteria but no SM and no CM detected     IgE-dependent allergy (or atopy)       Organ-specific variants       IgE-independent hypersensitivity reactions     Other Conditions       Reactive conditions (inflammation)       Toxic tissue damage (intoxication)       Physical, neurologic and others

iii. According to Frequency and Symptom-Free Intervals     Acute single event       With a known trigger (e.g., allergen)       Without a known trigger     Episodic recurrent       With a known trigger (e.g., allergen)       Without a known trigger     Chronic persistent       With a known trigger (e.g., allergen)       Without a known trigger

* Systemic MCA involves two or more organ systems.