2026 ICD-10-CM Diagnosis Code C91.51Adult T-cell lymphoma/leukemia (HTLV-1-associated), in remission

ICD-10-CM Codes›C00–D49›C81-C96›C91

ICD-10-CM C91.51
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

C91.51 is a billable ICD-10-CM diagnosis code for adult T-cell lymphoma/leukemia (HTLV-1-associated), in remission. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 820 through 825, 840 through 842. The code is restricted by the Medicare Code Editor to adult patients (age 15 through 124). Coders also document this condition as acute lymphoid leukemia in remission. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Leukemia in remission.

Code Identity

ICD-10-CM Code
C91.51
Billable Status
Yes — Valid for Submission
Code Describes
Adult T-cell lymphoma/leukemia (HTLV-1-associated), in remission
Short Description
Adult T-cell lymphoma/leukemia (HTLV-1-assoc), in remission
Parent Code
C91.5
Adult T-cell lymphoma/leukemia (HTLV-1-associated)

Code Classification

ChapterC00–D49Neoplasms
SectionC81-C96Malignant neoplasms of lymphoid, hematopoietic and related tissue
CategoryC91Lymphoid leukemia
This CodeC91.51Adult T-cell lymphoma/leukemia (HTLV-1-associated), in remission

Code EditsBilling

Medicare Code Editor checks that affect claim validity for C91.51.

Adult diagnoses
The Medicare Code Editor detects inconsistencies in adult cases by checking a patient's age and any diagnosis on the patient's record. The adult code edits apply to patients age range is 15–124 years inclusive (e.g., senile delirium, mature cataract).

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acute lymphoid leukemia in remission
  • Adult T-cell leukemia/lymphoma
  • Adult T-cell leukemia/lymphoma in remission
  • Lymphoid leukemia in remission
  • Malignant lymphoma in remission
  • Non-Hodgkin's lymphoma in remission

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NEO075
Leukemia in remission
Default principal diagnosis: inpatient Yes · outpatient Yes

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 C91.51 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
204.81 Oth lym leuk w rmsion
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About C91.51Overview

Is C91.51 (Adult T-cell lymphoma/leukemia (HTLV-1-associated)) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report adult T-cell lymphoma/leukemia (HTLV-1-associated), in remission on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does C91.51 group to?

When adult T-cell lymphoma/leukemia (HTLV-1-associated), in remission is the principal diagnosis on an inpatient stay, it groups to MS-DRG 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.

Who can C91.51 be reported for?

The Medicare Code Editor checks adult T-cell lymphoma/leukemia (HTLV-1-associated), in remission against patient demographics: this code is intended for adult patients (age 15 through 124). Claims outside these limits are flagged as inconsistent.

What is the ICD-9 equivalent of C91.51?

Under the General Equivalence Mappings, adult T-cell lymphoma/leukemia (HTLV-1-associated), in remission converts to ICD-9-CM 204.81 (oth lym leuk w rmsion). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.