D89.42: Idiopathic mast cell activation syndrome
D89.42 is the billable ICD-10-CM diagnosis code for Idiopathic mast cell activation syndrome. It is a fully specified code, so it can be reported on a claim (subject to clinical documentation and your payer's rules).
Frequently asked questions
What is ICD-10-CM code D89.42?
D89.42 is the ICD-10-CM diagnosis code for Idiopathic mast cell activation syndrome. It belongs to category D89 (Other disorders involving the immune mechanism, not elsewhere classified).
Is D89.42 a billable code?
Yes. D89.42 is a billable, fully specified ICD-10-CM code, so it can be used on a claim (subject to documentation and payer rules).
What category does D89.42 belong to?
D89.42 is part of ICD-10-CM category D89 — Other disorders involving the immune mechanism, not elsewhere classified, which has 48 billable codes.
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Informational only, not coding or medical advice. Verify against the official ICD-10-CM (FY2026) and your payer's guidelines.
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