Peripheral Blood KIT-D816V Mutation in Adult Systemic Mastocytosis

Inclusion Criteria: * Age \>= 18 years. * Presenting with recurrent idiopathic anaphylactic reactions (e.g., hypotension, syncope), mast cell activation syndrome (MCAS)-related symptoms (flushing, abdominal pain, diarrhea), urticaria pigmentosa, or histopathological findings of mast cell aggregation. * No prior treatment with KIT inhibitors or drugs affecting mast cell function (e.g., corticosteroids, interferon, immunosuppressants). * Willingness to undergo bone marrow examination and peripheral blood KIT-D816V testing, consent to biannual clinical follow-up for 6 months, and signing of the informed consent form. Exclusion Criteria: * Patients from whom specimens cannot be obtained (e.g., due to comorbidities or coagulation abnormalities preventing sufficient peripheral blood collection or bone marrow biopsy). * Prior diagnosis of other clonal hematologic diseases (e.g., other types of leukemia or lymphoid malignancies) that could interfere with the specificity of the KIT-D816V mutation assessment. * Treatment with targeted KIT drugs (e.g., imatinib, avapritinib) within the last 3 months. * Systemic corticosteroid, interferon, or immunosuppressive therapy within the last 1 month. * Refusal to participate or inability to complete follow-up due to severe comorbidities or other personal reasons.