ICD-10 Code D89.4 – Mast cell activation syndrome and related disorders (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code D89.4 – Mast cell activation syndrome and related disorders
What it is
D89.4 identifies mast cell activation syndrome and related mast cell activation disorders. Use it when the record documents abnormal mast cell mediator release causing recurrent, multisystem symptoms.
Clinical signs
Clinical features vary; refer to documentation. Commonly recorded findings include flushing, itching, hives, abdominal symptoms, and episodic reactions involving more than one organ system.
When to use this code
Use this code when the clinician specifically diagnoses mast cell activation syndrome or a related mast cell activation disorder. It is appropriate when the note links recurrent symptoms to mast cell mediator release. If the documentation is vague, check documentation before assigning the code.
Do not use for
Do not use D89.4 for isolated allergic reactions, anaphylaxis without mast cell activation syndrome, or other mast cell disorders not documented as related mast cell activation disease. Check documentation.
Coding tip
Code only when the provider names the disorder or clearly documents mast cell activation syndrome.