ICD-10-CM diagnosis code
C91.40 Hairy cell leukemia not having achieved remission
- Billable
- Yes, a complete code (FY2026)
- Category
- C91 Lymphoid leukaemia
- Chapter
- 2. Neoplasms
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Other codes in C91
27 complete codes in this category.
- C91.10Chronic lymphocytic leukemia of B-cell type not having achieved remission
- C91.11Chronic lymphocytic leukemia of B-cell type in remission
- C91.12Chronic lymphocytic leukemia of B-cell type in relapse
- C91.30Prolymphocytic leukemia of B-cell type not having achieved remission
- C91.31Prolymphocytic leukemia of B-cell type, in remission
- C91.32Prolymphocytic leukemia of B-cell type, in relapse
- C91.40Hairy cell leukemia not having achieved remission
- C91.41Hairy cell leukemia, in remission
- C91.42Hairy cell leukemia, in relapse
- C91.50Adult T-cell lymphoma/leukemia (HTLV-1-associated) not having achieved remission
- C91.51Adult T-cell lymphoma/leukemia (HTLV-1-associated), in remission
- C91.52Adult T-cell lymphoma/leukemia (HTLV-1-associated), in relapse
Documentation tips
- Make sure the note supports every element of the title, “Hairy cell leukemia not having achieved remission”: each detail in it should be traceable to the history, examination or assessment.
- Code to the highest specificity the documentation supports. If a detail is missing from the note, add it to the note rather than choosing a less specific code by default.
- Check the Tabular List and official guidelines for instructional notes (“code first”, “use additional code”, Excludes1/Excludes2) that apply to C91.
The international WHO ICD-10 also has C91, with its inclusion and exclusion notes; titles and detail can differ from ICD-10-CM.
ICD-10-CM is developed by the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention, U.S. Department of Health and Human Services, and is based on the WHO ICD-10. Codes and titles are reproduced unchanged from the FY2026 code list (effective 1 October 2025). Their use here does not imply endorsement by CDC, HHS or the U.S. Government. Changes effective on or after 1 October 2026 may not be reflected yet; check the current release at cdc.gov or cms.gov before submitting claims.
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