ICD-10 Code C91 – Lymphoid leukemia (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C91 – Lymphoid leukemia
What it is
C91 identifies lymphoid leukemia, a group of malignant disorders affecting lymphoid blood-forming cells. Use it when the record documents leukemia of lymphoid origin without a more specific subtype.
Clinical signs
Clinical features vary; refer to documentation. Commonly recorded findings include abnormal lymphocyte proliferation, marrow involvement, and signs of blood cell suppression. Confirm the provider’s stated leukemia type before coding.
When to use this code
Use C91 when the diagnosis is documented as lymphoid leukemia and no narrower ICD-10-CM code is specified. It may apply to initial diagnosis, follow-up visits, or encounters for ongoing management, as long as the condition remains active.
If the note names a specific lymphoid leukemia subtype, code that more specific entry instead. Check documentation when the record only says “leukemia” or uses unclear wording about lineage or chronicity.
Do not use for
Do not use C91 for myeloid leukemias, other specified leukemias, or leukemia in remission when a remission code is required. Do not assume lymphoid origin without provider documentation.
Coding tip
Look for the exact leukemia type in the assessment or pathology report before assigning C91.