C91.40
BillableHairy cell leukemia not having achieved remission
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C91.40 an HCC code?
Yes. C91.40 maps to Colorectal, Bladder, and Other Cancers under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for C91.40
For C91.40 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C91.40 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C91.40 is the ICD-10-CM diagnosis code for hairy cell leukemia not having achieved remission. A rare blood cancer (hairy cell leukemia) characterized by abnormal cells with hair-like projections that has not achieved remission. C91.40 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of lymphoid, hematopoietic and related tissue (c81-c96).
Under the CMS-HCC V28 risk adjustment model, C91.40 maps to Colorectal, Bladder, and Other Cancers (HCC 22) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, C91.40 maps to Lymphoma and Other Cancers (HCC 10) with a community, non-dual, aged base RAF weight of 0.675. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
Hairy cell leukemia is a distinct subtype of lymphoid leukemia; verify diagnosis before coding. Because C91.40 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for C91.40 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Hairy cell leukemia is a distinct subtype of lymphoid leukemia; verify diagnosis before coding
- •The fifth character '0' indicates no remission - document treatment response status
Clinical Significance
Hairy cell leukemia (HCL) is an indolent B-cell lymphoid neoplasm characterized by pancytopenia, splenomegaly, and distinctive 'hairy' cytoplasmic projections on malignant cells. Despite its indolent nature, untreated HCL can cause severe cytopenias and life-threatening infections. The 'not in remission' designation indicates active disease with ongoing bone marrow infiltration and potential symptomatic cytopenias.
Documentation Requirements
- ✓Documentation should include the characteristic morphology (hairy projections on light microscopy), immunophenotype (CD25+, CD103+, CD11c+, CD123+, Annexin A1+), and bone marrow biopsy findings showing a classic 'fried egg' pattern.
- ✓Disease status as not in remission must be explicitly stated, along with current blood counts showing cytopenias and spleen size assessment.