ICD-10 Code C91.40 – Hairy Cell Leukemia Not Having Achieved Remission (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C91.40 – Hairy cell leukemia not having achieved remission
What it is
C91.40 identifies hairy cell leukemia that has not reached remission. Use it when the record clearly states the disease is active or persistent after treatment, or when remission is specifically not achieved.
Clinical signs
Clinical features vary; refer to documentation. Hairy cell leukemia is a chronic B-cell leukemia that may present with cytopenias, splenomegaly, fatigue, or recurrent infections.
When to use this code
Use this code when the provider documents hairy cell leukemia as “not in remission,” “persistent,” or “active” after therapy. It also fits follow-up notes that confirm ongoing disease rather than remission status. Check documentation if the chart only says history of leukemia.
Do not use for
Do not use this code if the record states remission, complete response, or no evidence of disease. It is also incorrect for unspecified leukemia or when hairy cell leukemia is mentioned without current disease status.
Coding tip
Code the remission status exactly as documented; if it is unclear, query the provider rather than assuming active disease.