Systemic mastocytosis

This code represents a rare, chronic myeloproliferative neoplasm characterized by abnormal proliferation and accumulation of mast cells in various organs, most commonly the bone marrow, skin, gastrointestinal tract, and liver. It is a systemic disorder that can manifest with a wide range of symptoms due to mast cell mediator release and organ infiltration.

Use this code when documentation specifies a diagnosis of systemic mastocytosis without features indicating aggressive systemic mastocytosis or mast cell leukemia. This diagnosis is typically confirmed by bone marrow biopsy showing characteristic mast cell infiltrates and often by genetic testing for KIT D816V mutation.

• Ensure documentation explicitly states "systemic mastocytosis" and rules out aggressive forms or leukemia.
• Review pathology reports and genetic testing results for definitive diagnosis.
• Do not code with C96.21 (aggressive systemic mastocytosis) or C94.3- (mast cell leukemia) due to Excludes1 note.