What is ICD-10 code C91.A0?

C91.A0 is the ICD-10-CM diagnosis code for Mature B-cell leukemia Burkitt-type not having achieved remission. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C91.A0 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C91.A0 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.A0 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.A0 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.

What is the V28 vs V24 difference for C91.A0?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For C91.A0, V28 maps to Lung and Other Severe Cancers at RAF 0.000 while V24 mapped to Lymphoma and Other Cancers at RAF 0.675. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting C91.A0?

Verify the remission status in the medical record - this code specifically indicates the patient has NOT achieved remission, which is critical for accurate coding Do not use this code if the patient has achieved remission or complete response to treatment; instead use the appropriate remission code (C91.A1) Because C91.A0 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

C91.A0 ICD-10 Code: Mature B-cell leukemia

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.A0Effective 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.A0

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

Mature B-cell leukemia Burkitt-type not having achieved remission

This is a type of aggressive blood cancer called Burkitt leukemia that starts from immature B cells in the bone marrow and has not gone into remission (improvement). The cancer cells are actively present and the patient is undergoing or needs treatment.

Buddy Insight

CMS-HCC V28

Mapped

HCC 20

Lung and Other Severe Cancers

RAF 0.0

CMS-HCC V24

Mapped

HCC 10

Lymphoma and Other Cancers

RAF 0.675

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 10

Lymphoma and Other Cancers

RAF 0.0

RXHCC

Mapped

HCC 19

Lymphoma and Other Cancers

RAF 0.0

Code Trumping

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Code Book Path

Official

C91Lymphoid leukemia

C91.AMature B-cell leukemia Burkitt-type

C91.A0Mature B-cell leukemia Burkitt-type not having achieved remission

Inclusion Terms

Official

Mature B-cell leukemia Burkitt-type with failed remission
Mature B-cell leukemia Burkitt-type NOS

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C91.A0 in this effective period.

Related Child Codes

Official

C91.A1Mature B-cell leukemia Burkitt-type, in remission

C91.A2Mature B-cell leukemia Burkitt-type, in relapse

Includes

Official

ICD-10-CM does not list Includes notes for C91.A0 in this effective period.

Excludes 1

Official

Burkitt lymphoma (C83.7-)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C91.A0 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C91.A0 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C91.A0 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation must confirm the Burkitt-type morphology with characteristic cytogenetics, specifically t(8

14)(q24

q32) involving the MYC gene, or variant translocations t(2

8) or t(8

MEAT Support

HCC Buddy guidance

Documentation must confirm the Burkitt-type morphology with characteristic cytogenetics, specifically t(8

14)(q24

q32) involving the MYC gene, or variant translocations t(2

8) or t(8

Audit Caution

HCC Buddy guidance

The distinction between Burkitt leukemia and Burkitt lymphoma is based on the degree of bone marrow involvement (greater than 25% blasts = leukemia).

Do not confuse with diffuse large B-cell lymphoma, even with MYC rearrangement (double-hit lymphoma uses different codes).

The extremely rapid doubling time means disease status can change dramatically within days.

Ensure tumor lysis syndrome prophylaxis is documented.

Common Mistakes

HCC Buddy guidance

C83.70-C83.79 (Burkitt lymphoma) is used when disease predominantly involves lymph nodes and extranodal sites rather than bone marrow/blood.

C91.00 (acute lymphoblastic leukemia, not in remission) may be confused but lacks the specific Burkitt-type morphology and MYC translocation.

C91.90 (lymphoid leukemia, unspecified) is far less specific.

C91.Z0 (other lymphoid leukemia not in remission) should not be used when Burkitt-type is confirmed.

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is C91.A0 an HCC code?

Yes. C91.A0 maps to Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24).

HCC Category Mapping

V28HCC 20, Lung and Other Severe Cancers

0.000

V24HCC 10, Lymphoma and Other Cancers

0.675

ESRDHCC 10, Lymphoma and Other Cancers

0.000

RxHCCHCC 19, Lymphoma and Other Cancers

0.000

RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

MEAT Criteria for C91.A0

For C91.A0to 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.A0 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

C91.A0 is the ICD-10-CM diagnosis code for mature b-cell leukemia burkitt-type not having achieved remission. This is a type of aggressive blood cancer called Burkitt leukemia that starts from immature B cells in the bone marrow and has not gone into remission (improvement). The cancer cells are actively present and the patient is undergoing or needs treatment. C91.A0 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.A0 maps to Lung and Other Severe Cancers (HCC 20) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, C91.A0 maps to Lymphoma and Other Cancers (HCC 10) with a community, non-dual, aged base RAF weight of 0.675. 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.

Verify the remission status in the medical record - this code specifically indicates the patient has NOT achieved remission, which is critical for accurate coding. Because C91.A0 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. 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, RAF weights, and MEAT documentation criteria for C91.A0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Verify the remission status in the medical record - this code specifically indicates the patient has NOT achieved remission, which is critical for accurate coding
•Do not use this code if the patient has achieved remission or complete response to treatment; instead use the appropriate remission code (C91.A1)

Clinical Significance

Mature B-cell leukemia Burkitt-type (also known as Burkitt leukemia or L3 ALL) is an extremely aggressive hematologic malignancy characterized by rapidly proliferating mature B cells with a high mitotic index. This leukemia is closely related to Burkitt lymphoma and often presents with high tumor burden, tumor lysis syndrome risk, and central nervous system involvement. The 'not in remission' status indicates active, highly proliferative disease requiring urgent intensive chemotherapy.

Documentation Requirements

✓Documentation must confirm the Burkitt-type morphology with characteristic cytogenetics, specifically t(8
✓14)(q24
✓q32) involving the MYC gene, or variant translocations t(2
✓8) or t(8
✓22). Ki-67 proliferation index approaching 100% and starry-sky pattern on biopsy should be noted. Active disease status and tumor lysis syndrome risk stratification must be documented. Central nervous system evaluation results should be included.

Commonly Confused Codes

•C83.70-C83.79 (Burkitt lymphoma) is used when disease predominantly involves lymph nodes and extranodal sites rather than bone marrow/blood.
•C91.00 (acute lymphoblastic leukemia, not in remission) may be confused but lacks the specific Burkitt-type morphology and MYC translocation.
•C91.90 (lymphoid leukemia, unspecified) is far less specific.
•C91.Z0 (other lymphoid leukemia not in remission) should not be used when Burkitt-type is confirmed.