This is a multi-center screening study with the primary objective to determine the prevalence of KIT D816V mutation in peripheral blood in patients with evidence of systemic mast cell activation (MCA).

Inclusion Criteria:

• Presenting with at least one of the three criteria below as evidence of systemic mast cell activation:

  1. Involvement of 2 or more organ systems, characterized by skin (pruritus, urticaria, flushing and angioedema), cardiovascular (tachycardia, syncope, and hypotension), gastrointestinal (diarrhea, nausea, vomiting, and gastrointestinal cramping) or respiratory/naso-ocular (wheezing, conjunctival injection, and nasal stuffiness) AND serum basal tryptase levels ≥8 ng/ml. One of the organ systems must be the cardiovascular system.
  2. Severe anaphylaxis (Ring and Messmer grading ≥II) due to Hymenoptera sting, regardless of serum basal tryptase levels.
  3. Severe anaphylaxis (Ring and Messmer grading ≥II), with cardiovascular involvement and documented event-related tryptase elevation fitting the formula 20% of baseline plus 2 ng/ml evaluated in at least 1 event.

Exclusion Criteria:

• Patient previously diagnosed with any of the following WHO systemic mastocytosis (SM) sub-classifications: mastocytosis in the skin, indolent SM, smoldering SM, SM with associated hematological neoplasm, aggressive SM, mast cell leukemia, mast cell sarcoma

Adult patients with systemic mast cell activation