Idiopathic mast cell activation syndrome

This code signifies a rare, chronic disorder characterized by recurrent episodes of systemic mast cell mediator release without an identifiable underlying cause. Patients experience a wide range of symptoms affecting multiple organ systems, including dermatologic, gastrointestinal, cardiovascular, and respiratory manifestations. The diagnosis is based on clinical criteria and laboratory evidence of mast cell activation.

Use this code when documentation explicitly states a diagnosis of "idiopathic mast cell activation syndrome" or "MCAS, idiopathic." This diagnosis is typically made by an allergist, immunologist, or hematologist after excluding secondary causes of mast cell activation. Supporting documentation should include clinical findings consistent with MCAS and laboratory evidence of mast cell mediator release.

• Distinguish from mastocytosis (D89.3) and secondary mast cell activation syndromes, which have different underlying etiologies.
• Ensure documentation specifies "idiopathic" to differentiate from other forms of MCAS.
• Code all associated symptoms and manifestations in addition to this primary diagnosis.