2026 ICD-10-CM Diagnosis Code C84.91Mature T/NK-cell lymphomas, unspecified, lymph nodes of head, face, and neck
ICD-10-CM Codes›C00–D49›C81-C96›C84
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 20
- Chronic Condition
C84.91 is a billable ICD-10-CM diagnosis code for mature T/NK-cell lymphomas, unspecified, lymph nodes of head, face, and neck. 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, 974 through 976. 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 70 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Non-Hodgkin lymphoma.
For Medicare Advantage risk adjustment, C84.91 maps to CMS-HCC Category 20 (Lung and Other Severe Cancers) under the V28 model, adding a risk factor of about 1.136 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
C84.91 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.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Lymphoma
Lymphoma is a cancer of a part of the immune system called the lymph system. There are many types of lymphoma. One type is Hodgkin disease. The rest are called non-Hodgkin lymphomas.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert C84.91 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About C84.91Overview
Is C84.91 (Mature T/NK-cell lymphomas, unspecified) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report mature T/NK-cell lymphomas, unspecified, lymph nodes of head, face, and neck on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does C84.91 group to?
When mature T/NK-cell lymphomas, unspecified, lymph nodes of head, face, and neck 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, 974, 975, 976, with relative weights from 0.8945 to 5.8648 depending on complications. Higher weights mean higher Medicare reimbursement.
Is C84.91 a CC or MCC?
CMS lists C84.91 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 70 closely related codes in its exclusion list.
What is the ICD-9 equivalent of C84.91?
Under the General Equivalence Mappings, mature T/NK-cell lymphomas, unspecified, lymph nodes of head, face, and neck converts to ICD-9-CM 202.81 (lymphomas NEC head). The mapping is approximate, so confirm the match fits the documentation.
What HCC is C84.91?
C84.91 (mature T/NK-cell lymphomas, unspecified, lymph nodes of head, face, and neck) maps to CMS-HCC Category 20 (Lung and Other Severe Cancers), commonly written as HCC 20, 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 C84.91 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, C84.91 adds a risk adjustment factor of about 1.136 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.672 to 1.214 depending on the payment segment). A more severe related category (HCC 17, HCC 18, and HCC 19) supersedes it when both are reported. See the full factor table on the HCC 20 category page.
