C94.31 maps to CMS-HCC V28 20. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC coding software

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Code lookupC94.31

Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C94.31

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

Mast cell leukemia, in remission

A rare blood cancer where mast cells multiply uncontrollably in the bone marrow and blood, and the cancer has responded well to treatment.

Buddy Insight

Mast cell leukemia in remission is exceptionally rare given the aggressive biology and limited treatment options for this disease.

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

Mapped

HCC 20

Lung and Other Severe Cancers

Coefficient HCC 20: 1.136 (Community Non-Dual Aged (CNA))

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 009

HHS-HCC 009 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 9

Lung and Other Severe Cancers

Code-level coefficient reference

RXHCC

Mapped

HCC 19

Leukemias and Other Hematolog...

Code-level coefficient reference

Code Book Path

Official

C94Other leukemias of specified cell type C94.3Mast cell leukemia C94.31Mast cell leukemia, in remission

Inclusion Terms

Official

No inclusion terms are included in this display for C94.31. Check the code and parent instructions in the Code Book.

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

C94.30Mast cell leukemia not having achieved remission C94.32Mast cell leukemia, in relapse

Includes

Official

No Includes notes are included in this display for C94.31. Check the code and parent instructions in the Code Book.

Excludes 1

Official

leukemic reticuloendotheliosis (C91.4-)Inherited from C94
myelodysplastic syndromes (D46.-)Inherited from C94
personal history of leukemia (Z85.6)Inherited from C94
plasma cell leukemia (C90.1-)Inherited from C94

Code First

Official

No Code First sequencing instructions are included in this display for C94.31. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for C94.31. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for C94.31. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance

Remission documentation should include resolution or significant reduction of bone marrow mast cell infiltration, normalization of serum tryptase levels, absence of circulating mast cells, and resolution of organ damage.

The specific therapy that achieved remission and ongoing surveillance plan must be recorded.

MEAT Support

HCC Buddy guidance

The specific therapy that achieved remission and ongoing surveillance plan must be recorded.

Audit Caution

HCC Buddy guidance

Given the extreme rarity of remission in mast cell leukemia, ensure documentation robustly supports this status with objective evidence.

Partial responses should not be coded as remission.

If only organ damage resolves but mast cell burden persists, remission may not be appropriate.

Common Mistakes

HCC Buddy guidance

C94.30 (not achieved remission) and C94.32 (in relapse) represent different treatment phases.

C96.21 (aggressive systemic mastocytosis) is a different stage of mast cell disease.

D47.02 (systemic mastocytosis) is the indolent form without leukemic progression.

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 C94.31 an HCC code?

Yes. C94.31 (Mast cell leukemia, in remission) maps to HCC 20, Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 1.136. 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: C94.31 is billable and maps to V28 HCC 20, Lung and Other Severe Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C94.31
Description: Mast cell leukemia, in remission
HCC (V28): HCC 20 — Lung and Other Severe Cancers
RAF reference coefficient: 1.136
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 20, Lung and Other Severe Cancers

1.136

ESRDHCC 9, Lung and Other Severe 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 C94.31 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C94.31

For C94.31, 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

C94.31 is the ICD-10-CM diagnosis code for mast cell leukemia, in remission. A rare blood cancer where mast cells multiply uncontrollably in the bone marrow and blood, and the cancer has responded well to treatment. C94.31 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, C94.31 maps to Lung and Other Severe Cancers (HCC 20) with a source-labeled community, non-dual, aged reference coefficient of 1.136. 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 C94.31 when the provider wording supports mast cell leukemia, in remission. Check the FY2026 tabular notes and the full code path before the final code choice. For C94.31, 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 C94.31 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Use C94.31 when the provider wording supports mast cell leukemia, in 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 mast cell leukemia, in remission. Keep the checklist tied to the note.
•Do not swap C94.31 with C94.30. The FY2026 tabular describes C94.30 as mast cell leukemia not having achieved remission. Follow the documented detail.
•C94.31 maps to V28 HCC 20, Lung and Other Severe 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 C94.31 or compare its code path with C94.30.

Clinical Significance

Mast cell leukemia in remission is exceptionally rare given the aggressive biology and limited treatment options for this disease. Remission achievement typically requires novel targeted therapies such as midostaurin or avapritinib, and sustained remission is uncommon, making each case clinically remarkable.

Documentation Requirements

✓Remission documentation should include resolution or significant reduction of bone marrow mast cell infiltration, normalization of serum tryptase levels, absence of circulating mast cells, and resolution of organ damage.
✓The specific therapy that achieved remission and ongoing surveillance plan must be recorded.

Commonly Confused Codes

•C94.30 (not achieved remission) and C94.32 (in relapse) represent different treatment phases.
•C96.21 (aggressive systemic mastocytosis) is a different stage of mast cell disease.
•D47.02 (systemic mastocytosis) is the indolent form without leukemic progression.