C91.40 maps to CMS-HCC V28 22. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC coding software

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Code lookupC91.40

Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of lymphoid, hematopoietic and related tissue (C81-C96)

C91.40

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

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.

Buddy Insight

Hairy cell leukemia (HCL) is an indolent B-cell lymphoid neoplasm characterized by pancytopenia, splenomegaly, and distinctive 'hairy' cytoplasmic projections on malignant cells.

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

Mapped

HCC 22

Bladder, Colorectal, and Othe...

Coefficient HCC 22: 0.363 (Community Non-Dual Aged (CNA))

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 010

HHS-HCC 010 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 10

Lymphoma and Other Cancers

Code-level coefficient reference

RXHCC

Mapped

HCC 21

Lymphomas and Other Hematolog...

Code-level coefficient reference

Code Book Path

Official

C91Lymphoid leukemia C91.4Hairy cell leukemia C91.40Hairy cell leukemia not having achieved remission

Inclusion Terms

Official

Hairy cell leukemia with failed remission
Hairy cell leukemia NOS
Leukemic reticuloendotheliosisInherited from C91.4

Excludes 2

Official

Kaposi's sarcoma of lymph nodes (C46.3)Inherited from C81-C96
secondary and unspecified neoplasm of lymph nodes (C77.-)Inherited from C81-C96
secondary neoplasm of bone marrow (C79.52)Inherited from C81-C96
secondary neoplasm of spleen (C78.89)Inherited from C81-C96

Related Codes

Official

C91.41Hairy cell leukemia, in remission C91.42Hairy cell leukemia, in relapse

Includes

Official

No Includes notes are included in this display for C91.40. Check the code and parent instructions in the Code Book.

Excludes 1

Official

personal history of leukemia (Z85.6)Inherited from C91

Code First

Official

No Code First sequencing instructions are included in this display for C91.40. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for C91.40. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for C91.40. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance

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.

MEAT Support

HCC Buddy guidance

Disease status as not in remission must be explicitly stated, along with current blood counts showing cytopenias and spleen size assessment.

Audit Caution

HCC Buddy guidance

HCL has an excellent prognosis with first-line therapy (cladribine or pentostatin), achieving remission in over 90% of patients.

Ensure the 'not in remission' status is current and accurate, as many patients will achieve remission after treatment.

Do not confuse HCL with HCL variant, which has a different prognosis and treatment approach.

Tartrate-resistant acid phosphatase (TRAP) positivity alone is insufficient for diagnosis.

Common Mistakes

HCC Buddy guidance

C91.10 (B-CLL not in remission) is the most common misassignment, as both are indolent B-cell leukemias. HCL variant (HCLv) is a distinct entity with different immunophenotype and should be coded under C91.Z

C91.90 (lymphoid leukemia, unspecified) should not be used when HCL is specifically diagnosed. Splenic marginal zone lymphoma (C83.0) may mimic HCL clinically.

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is C91.40 an HCC code?

Yes. C91.40 (Hairy cell leukemia not having achieved remission) maps to HCC 22, Bladder, Colorectal, and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.363. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: C91.40 is billable and maps to V28 HCC 22, Bladder, Colorectal, and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C91.40
Description: Hairy cell leukemia not having achieved remission
HCC (V28): HCC 22 — Bladder, Colorectal, and Other Cancers
RAF reference coefficient: 0.363
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 22, Bladder, Colorectal, and Other Cancers

0.363

ESRDHCC 10, Lymphoma and Other Cancers

Not separately weighted

RxHCCHCC 21, Lymphomas and Other Hematologic Cancers

Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work C91.40 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C91.40

For C91.40, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

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

Coder workflow notes

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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 Bladder, Colorectal, and Other Cancers (HCC 22) with a source-labeled community, non-dual, aged reference coefficient of 0.363. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Hairy cell leukemia is a distinct subtype of lymphoid leukemia; verify diagnosis before coding. For C91.40, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, 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.

Commonly Confused Codes

•C91.10 (B-CLL not in remission) is the most common misassignment, as both are indolent B-cell leukemias. HCL variant (HCLv) is a distinct entity with different immunophenotype and should be coded under C91.Z
•C91.90 (lymphoid leukemia, unspecified) should not be used when HCL is specifically diagnosed. Splenic marginal zone lymphoma (C83.0) may mimic HCL clinically.