What is ICD-10 code C91.61?

C91.61 is the ICD-10-CM diagnosis code for Prolymphocytic leukemia of T-cell type, in remission. A rare blood cancer (prolymphocytic leukemia) affecting T-cells that has responded to treatment and is in remission. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C91.61 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C91.61 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C91.61 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C91.61 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does C91.61 map to under V28?

C91.61 maps to CMS-HCC V28 HCC 19 (Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

2026 ICD-10-CM C91.61: Prolymphocytic leukemia

C91.61 maps to CMS-HCC V28 19. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC coding software

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupC91.61Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C91.61

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

Prolymphocytic leukemia of T-cell type, in remission

A rare blood cancer (prolymphocytic leukemia) affecting T-cells that has responded to treatment and is in remission.

Buddy Insight

T-cell prolymphocytic leukemia in remission indicates that this rare aggressive T-cell malignancy has responded to treatment, most commonly alemtuzumab-based therapy.

CMS-HCC V28

Mapped

HCC 19

Myelodysplastic Syndromes, Mu...

Code-level coefficient reference

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 19

Leukemias and Other Hematolog...

Code-level coefficient reference

Code Book Path

Official

C91Lymphoid leukemia

C91.6Prolymphocytic leukemia of T-cell type

C91.61Prolymphocytic leukemia of T-cell type, in remission

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C91.61 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C91.61 in this effective period.

Related Child Codes

Official

C91.60Prolymphocytic leukemia of T-cell type not having achieved remission

C91.62Prolymphocytic leukemia of T-cell type, in relapse

Includes

Official

ICD-10-CM does not list Includes notes for C91.61 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C91.61 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C91.61 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C91.61 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C91.61 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

The provider must document the remission status explicitly, including whether complete or partial remission has been achieved.

Treatment regimen and date of remission should be recorded.

Documentation should include plans for consolidation (transplant evaluation) and surveillance frequency.

Updated flow cytometry and imaging at remission assessment should be noted.

MEAT Support

HCC Buddy guidance

The provider must document the remission status explicitly, including whether complete or partial remission has been achieved.

Treatment regimen and date of remission should be recorded.

Documentation should include plans for consolidation (transplant evaluation) and surveillance frequency.

Updated flow cytometry and imaging at remission assessment should be noted.

Audit Caution

HCC Buddy guidance

Remission in T-PLL is typically brief, so verify current status at each encounter. Do not confuse stable disease on therapy with remission -

specific criteria must be met. Patients proceeding to transplant while in remission still use this code until disease status changes. Spontaneous remission in T-PLL is exceedingly rare; ensure treatment response documentation.

Common Mistakes

HCC Buddy guidance

C91.60 (T-PLL not in remission) is for active disease.

C91.62 (T-PLL in relapse) is for recurrent disease.

C91.31 (B-cell prolymphocytic leukemia in remission) is the B-cell counterpart.

C91.51 (ATLL in remission) is a different HTLV-1-associated entity.

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 C91.61 an HCC code?

Yes. C91.61 (Prolymphocytic leukemia of T-cell type, in remission) maps to HCC 19, Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 1.798. 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: C91.61 is billable and maps to V28 HCC 19, Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C91.61
Description: Prolymphocytic leukemia of T-cell type, in remission
HCC (V28): HCC 19 — Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers
RAF reference coefficient: 1.798
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 19, Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers

1.798

ESRDHCC 10, Lymphoma and Other Cancers

Not separately weighted

RxHCCHCC 19, Leukemias 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 C91.61 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for C91.61

For C91.61 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 C91.61 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C91.61 is the ICD-10-CM diagnosis code for prolymphocytic leukemia of t-cell type, in remission. A rare blood cancer (prolymphocytic leukemia) affecting T-cells that has responded to treatment and is in remission. C91.61 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, C91.61 maps to Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers (HCC 19) with a source-labeled community, non-dual, aged reference coefficient of 1.798. No V24 mapping is shown for C91.61; use the applicable model and payment year when reviewing the V28 mapping. 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. 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.

The fifth character '1' indicates remission status - confirm remission documentation. Because C91.61 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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 C91.61 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•The fifth character '1' indicates remission status - confirm remission documentation
•T-cell prolymphocytic leukemia is distinct from B-cell type; verify cell type in diagnosis

Clinical Significance

T-cell prolymphocytic leukemia in remission indicates that this rare aggressive T-cell malignancy has responded to treatment, most commonly alemtuzumab-based therapy. Remission in T-PLL is achievable but typically short-lived without consolidation with allogeneic stem cell transplantation. Ongoing surveillance is critical due to the high probability of relapse within months of achieving remission.

Documentation Requirements

✓The provider must document the remission status explicitly, including whether complete or partial remission has been achieved.
✓Treatment regimen and date of remission should be recorded.
✓Documentation should include plans for consolidation (transplant evaluation) and surveillance frequency.
✓Updated flow cytometry and imaging at remission assessment should be noted.

Commonly Confused Codes

•C91.60 (T-PLL not in remission) is for active disease.
•C91.62 (T-PLL in relapse) is for recurrent disease.
•C91.31 (B-cell prolymphocytic leukemia in remission) is the B-cell counterpart.
•C91.51 (ATLL in remission) is a different HTLV-1-associated entity.