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C91.90 ICD-10-CM Code: Lymphoid leukemia, unspecified not having achieved remission

C91.90 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 Buddy coding tools

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Code lookupC91.90

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

C91.90

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

Lymphoid leukemia, unspecified not having achieved remission

A type of blood cancer affecting lymphoid cells that has not gone into remission or is actively progressing.

Buddy the Bee presenting code insight

Buddy Insight

Lymphoid leukemia, unspecified, not in remission is a nonspecific code used when the exact subtype of lymphoid leukemia cannot be determined but active disease is present.

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

HCC 22

Code-level coefficient reference

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 010

Code-level coefficient reference

ESRD/PACE

HCC 10

Code-level coefficient reference

RXHCC

HCC 19

Code-level coefficient reference

Code Book Path

Official
C91Lymphoid leukemiaC91.9Lymphoid leukemia, unspecifiedC91.90Lymphoid leukemia, unspecified not having achieved remission

Inclusion Terms

Official
  • Lymphoid leukemia with failed remission
  • Lymphoid leukemia NOS

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
C91.91Lymphoid leukemia, unspecified, in remissionC91.92Lymphoid leukemia, unspecified, in relapse

Includes

Official

No Includes notes are included in this display for C91.90. 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 C91.90. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for C91.90. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for C91.90. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance
While this code is used for unspecified lymphoid leukemia, documentation efforts should aim to obtain the specific subtype through immunophenotyping, cytogenetics, and molecular studies.
The active disease status (not in remission) must be documented.
Any available diagnostic information, even if incomplete, should be recorded to support potential reclassification to a more specific code.

MEAT Support

HCC Buddy guidance
While this code is used for unspecified lymphoid leukemia, documentation efforts should aim to obtain the specific subtype through immunophenotyping, cytogenetics, and molecular studies.
The active disease status (not in remission) must be documented.
Any available diagnostic information, even if incomplete, should be recorded to support potential reclassification to a more specific code.

Audit Caution

HCC Buddy guidance
This code should be a last resort when subtype cannot be determined.
Query the provider before defaulting to this unspecified code, as most modern hematology workups can identify the specific subtype.
This code may be appropriate for initial encounters before complete diagnostic workup is available but should be updated once results return.
Using this code long-term may indicate incomplete diagnostic evaluation.

Common Mistakes

HCC Buddy guidance
More specific codes should always be used when available: C91.10 (B-CLL), C91.00 (ALL, not in remission), C91.30 (B-PLL), C91.40 (HCL), or other specified subtypes.
C91.Z0 (other lymphoid leukemia not in remission) is for specified types not classified elsewhere.
C95.90 (leukemia, unspecified) is even less specific and should not be used when the lymphoid lineage is confirmed.

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 C91.90 an HCC code?

Yes. C91.90 (Lymphoid leukemia, unspecified 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: C91.90 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
C91.90
Description
Lymphoid leukemia, unspecified 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 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 C91.90 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C91.90

For C91.90, 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

C91.90 is the ICD-10-CM diagnosis code for lymphoid leukemia, unspecified not having achieved remission. A type of blood cancer affecting lymphoid cells that has not gone into remission or is actively progressing. C91.90 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, C91.90 maps to Bladder, Colorectal, and Other Cancers (HCC 22) with a source-labeled community, non-dual, aged reference coefficient of 0.363. No V24 mapping is shown for C91.90; use the applicable model and payment year when reviewing the V28 mapping. 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.

Use C91.90 when the provider wording supports lymphoid leukemia, unspecified not having achieved remission. Check the FY2026 tabular notes and the full code path before the final code choice. For C91.90, 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 C91.90 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Use C91.90 when the provider wording supports lymphoid leukemia, unspecified not having achieved remission. Check the FY2026 tabular notes and the full code path before the final code choice.
  • •For this DOS, capture the provider's current assessment and the care action documented for lymphoid leukemia, unspecified not having achieved remission. Keep the checklist tied to the note.
  • •Do not swap C91.90 with C91.91. The FY2026 tabular describes C91.91 as lymphoid leukemia, unspecified, in remission. Follow the documented detail.
  • •C91.90 maps to V28 HCC 22, Bladder, Colorectal, and Other Cancers. The mapping does not replace the documentation review. The code still has to match the note.
  • •Ask Buddy to show the official notes for C91.90 or compare its code path with C91.91.

Clinical Significance

Lymphoid leukemia, unspecified, not in remission is a nonspecific code used when the exact subtype of lymphoid leukemia cannot be determined but active disease is present. This code should be used sparingly and only when documentation lacks sufficient specificity to assign a more precise code. Unspecified codes may trigger medical record reviews and can indicate incomplete diagnostic workup.

Documentation Requirements

  • ✓While this code is used for unspecified lymphoid leukemia, documentation efforts should aim to obtain the specific subtype through immunophenotyping, cytogenetics, and molecular studies.
  • ✓The active disease status (not in remission) must be documented.
  • ✓Any available diagnostic information, even if incomplete, should be recorded to support potential reclassification to a more specific code.

Commonly Confused Codes

  • •More specific codes should always be used when available: C91.10 (B-CLL), C91.00 (ALL, not in remission), C91.30 (B-PLL), C91.40 (HCL), or other specified subtypes.
  • •C91.Z0 (other lymphoid leukemia not in remission) is for specified types not classified elsewhere.
  • •C95.90 (leukemia, unspecified) is even less specific and should not be used when the lymphoid lineage is confirmed.

Child Codes

C91.90Lymphoid leukemia, unspecified not having achieved remission
HCC 22
C91.91Lymphoid leukemia, unspecified, in remission
HCC 22
C91.92Lymphoid leukemia, unspecified, in relapse
HCC 22

Code Hierarchy

└C91Lymphoid leukemia└C91.9Lymphoid leukemia, unspecified└C91.90Lymphoid leukemia, unspecified not having achieved remission
└C91.90Lymphoid leukemia, unspecified not having achieved remission

For C91.90, 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.

C91.90 maps to CMS-HCC V28 category 22, Bladder, Colorectal, and Other Cancers. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for C91.90. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

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