C91.42
BillableHairy cell leukemia, in relapse
HCC Category Mapping
V28HCC 22 — Colorectal, Bladder, and Other Cancers
0.000V24HCC 10 — Lymphoma and Other Cancers
0.675ESRDHCC 10 — Lymphoma and Other Cancers
0.000RxHCCHCC 21 — Hodgkin Lymphoma and Other Cancers
0.000What This Code Means
A rare blood cancer (hairy cell leukemia) with hair-like abnormal cells that has returned after a period of remission.
Coding Tips
- •The fifth character '2' indicates relapse - ensure documentation shows cancer has recurred
- •Document timing and circumstances of relapse when available
Clinical Significance
Hairy cell leukemia in relapse indicates recurrence of disease after a prior period of documented remission. Relapsed HCL may present with recurrent cytopenias, re-enlargement of the spleen, or bone marrow re-infiltration. Second remissions are achievable with the same purine analog or alternative agents (rituximab, vemurafenib for BRAF V600E-mutated cases), though duration of subsequent remissions may be shorter.
Documentation Requirements
- ✓Documentation must establish prior remission and current evidence of disease recurrence, including rising hairy cells in blood or bone marrow, returning cytopenias, or splenic re-enlargement.
- ✓The interval since last remission, BRAF V600E mutation status (if tested), and planned treatment approach should be recorded.
- ✓Updated immunophenotyping at relapse helps confirm diagnosis and rule out other entities.
Commonly Confused Codes
C91.40 (HCL not in remission) is for disease that never achieved remission.C91.41 (HCL in remission) applies when disease is controlled.C91.12 (B-CLL in relapse) should not be used for relapsed HCL.C91.Z2 (other lymphoid leukemia in relapse) is less specific and should be avoided when HCL is confirmed.
Code Hierarchy
└C91Lymphoid leukemia└C91.4Hairy cell leukemia└C91.42Hairy cell leukemia, in relapse
└C91.42Hairy cell leukemia, in relapse