ICD-10 Code C91.12 – Chronic lymphocytic leukemia of B-cell type in relapse (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C91.12 – Chronic lymphocytic leukemia of B-cell type in relapse
What it is
C91.12 identifies chronic lymphocytic leukemia, B-cell type, that has returned after a prior remission or response. Use it when the record clearly documents relapse of CLL.
Clinical signs
Clinical features vary; refer to documentation. Commonly reported findings may include recurrent lymphocytosis, enlarged lymph nodes, splenomegaly, or other evidence that the leukemia has reappeared.
When to use this code
Use this code when the provider states the patient has relapsed B-cell chronic lymphocytic leukemia. It is appropriate in follow-up or oncology visits where recurrence is documented after prior disease control. If the note only says CLL without relapse status, check documentation.
Do not use for
Do not use C91.12 for newly diagnosed CLL or for remission status without relapse. If the record describes another leukemia type or the relapse is not documented, choose the more specific confirmed diagnosis.
Coding tip
Code relapse only when the provider explicitly documents recurrence, not when disease is merely being monitored.