2026 ICD-10-CM Diagnosis Code C91.40Hairy cell leukemia not having achieved remission
ICD-10-CM Codes›C00–D49›C81-C96›C91
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 22
- Chronic Condition
C91.40 is a billable ICD-10-CM diagnosis code for hairy cell leukemia not having achieved remission. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 11 through 13, 820 through 825, 840 through 842. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 49 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Leukemia - hairy cell.
For Medicare Advantage risk adjustment, C91.40 maps to CMS-HCC Category 22 (Bladder, Colorectal, and Other Cancers) under the V28 model, adding a risk factor of about 0.363 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
C91.40 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Atypical hairy cell leukemia
- Hairy cell leukemia
- Hairy cell leukemia of spleen
- Hairy cell leukemia variant
- Leukemic infiltration of skin
- Leukemic infiltration of skin in hairy-cell leukemia
- Leukemic reticuloendotheliosis of intra-abdominal lymph nodes
- Leukemic reticuloendotheliosis of intrapelvic lymph nodes
- Leukemic reticuloendotheliosis of intrathoracic lymph nodes
- Leukemic reticuloendotheliosis of lymph nodes of axilla and upper limb
- Leukemic reticuloendotheliosis of lymph nodes of head, face and neck
- Leukemic reticuloendotheliosis of lymph nodes of inguinal region and lower limb
- Leukemic reticuloendotheliosis of lymph nodes of multiple sites
- Metastatic malignant neoplasm to intrapelvic lymph nodes
- Metastatic malignant neoplasm to intrathoracic lymph nodes
- Metastatic malignant neoplasm to lymph nodes of lower limb
- Metastatic malignant neoplasm to lymph nodes of multiple sites
- Metastatic malignant neoplasm to lymph nodes of upper limb
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Hairy cell leukemia with failed remission
- Hairy cell leukemia NOS
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Leukemia
Leukemia is a term for cancers of the blood cells. Leukemia starts in blood-forming tissues such as the bone marrow. Your bone marrow makes the cells which will develop into white blood cells, red blood cells, and platelets. Each type of cell has a different job:
The full article covers:
- What is leukemia?
- What are the types of leukemia?
- What causes leukemia?
- Who is at risk for leukemia?
- What are the symptoms of leukemia?
- How is leukemia diagnosed?
- What are the treatments for leukemia?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert C91.40 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About C91.40Overview
What is the ICD-10 code for hairy cell leukemia not having achieved remission?
The ICD-10-CM code for hairy cell leukemia not having achieved remission is C91.40 (sometimes written as C9140). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is C91.40 (Hairy cell leukemia) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report hairy cell leukemia not having achieved remission on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does C91.40 group to?
When hairy cell leukemia not having achieved remission is the principal diagnosis on an inpatient stay, it groups to MS-DRG 11, 12, 13, 820, 821, 822, 823, 824, 825, 840, 841, 842, with relative weights from 1.0104 to 5.8648 depending on complications. Higher weights mean higher Medicare reimbursement.
Is C91.40 a CC or MCC?
CMS lists C91.40 as a CC (complication or comorbidity) for FY 2026. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 49 closely related codes in its exclusion list.
What is the ICD-9 equivalent of C91.40?
Under the General Equivalence Mappings, hairy cell leukemia not having achieved remission converts to ICD-9-CM 202.40 (lk rtctl unsp xtrndl org). The mapping is approximate, so confirm the match fits the documentation.
What HCC is C91.40?
C91.40 (hairy cell leukemia not having achieved remission) maps to CMS-HCC Category 22 (Bladder, Colorectal, and Other Cancers), commonly written as HCC 22, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 10 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 21.
Does C91.40 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, C91.40 adds a risk adjustment factor of about 0.363 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.314 to 0.410 depending on the payment segment). A more severe related category (HCC 17, HCC 18, HCC 19, HCC 20, and HCC 21) supersedes it when both are reported. See the full factor table on the HCC 22 category page.
