ICD-10 Code C91.4 – Hairy Cell Leukemia (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C91.4 – Hairy cell leukemia
What it is
C91.4 identifies hairy cell leukemia, a rare chronic B-cell leukemia. Use it when documentation states this specific diagnosis.
Clinical signs
Clinical features vary; refer to documentation. Commonly noted findings include splenomegaly, cytopenias, and abnormal lymphoid cells with “hairy” projections.
When to use this code
Use C91.4 when the provider documents hairy cell leukemia, including initial diagnosis, follow-up care, or ongoing management. Code it from confirmed clinical documentation, pathology, or hematology assessment. If the record only says leukemia without subtype, check documentation.
Do not use for
Do not use this code for other leukemias, lymphomas, or nonspecific “leukemia” diagnoses. If the subtype is unclear or different, verify the exact hematologic diagnosis first.
Coding tip
Capture the exact leukemia subtype from the chart, because C91.4 is specific to hairy cell leukemia.