ICD-10 Code D89.49 – Other mast cell activation disorder (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code D89.49 – Other mast cell activation disorder
What it is
D89.49 identifies other mast cell activation disorder, a condition where mast cells release mediators inappropriately. Use it when documentation names this disorder but does not specify a more exact mast cell diagnosis.
Clinical signs
Clinical features vary; refer to documentation. Commonly reported findings include recurrent flushing, itching, hives, abdominal complaints, or other episodic mediator-related symptoms.
When to use this code
Use D89.49 when the provider documents other mast cell activation disorder and the record supports the diagnosis. It is appropriate when the condition is confirmed, but the note does not identify a more specific mast cell activation subtype.
Code it from specialist assessments, problem lists, or discharge summaries only when the diagnosis is clearly stated. If the chart is vague or suggests possible mast cell disease without confirmation, check documentation before assigning the code.
Do not use for
Do not use this code for generalized allergic reactions, urticaria alone, or anaphylaxis unless the provider specifically documents mast cell activation disorder. Do not assume it from symptoms without a stated diagnosis.
Coding tip
Confirm the exact wording in the assessment or final diagnosis; if a more specific mast cell disorder is documented, choose that code instead.