What is ICD-10 code D46.21?

D46.21 is the ICD-10-CM diagnosis code for Refractory anemia with excess of blasts 1. A bone marrow disorder where red blood cells cannot be produced normally and there is an excess of immature blood cells at 5-9% of the bone marrow. D46.21 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. D46.21 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. D46.21 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. D46.21 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 D46.21?

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 D46.21, V28 maps to Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers at RAF 1.798 while V24 mapped to Severe Hematological Disorders at RAF 1.372. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting D46.21?

Requires documentation of blast percentage between 5-9% Distinguish from D46.22 which indicates 10-19% blasts Because D46.21 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.

2026 ICD-10-CM D46.21: Refractory anemia

ICD-10-CM Code View

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Code lookupD46.21Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Neoplasms of uncertain behavior, polycythemia vera and myelodysplastic syndromes (D37-D48)

D46.21

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

Refractory anemia with excess of blasts 1

A bone marrow disorder where red blood cells cannot be produced normally and there is an excess of immature blood cells at 5-9% of the bone marrow.

Buddy Insight

Refractory anemia with excess of blasts 1 (RAEB-1) is a higher-risk myelodysplastic syndrome subtype with 5-9% blasts in the bone marrow.

CMS-HCC V28

Mapped

HCC 19

Myelodysplastic Syndromes, Mu...

RAF 1.798

CMS-HCC V24

Mapped

HCC 46

Severe Hematological Disorders

RAF 1.372

ACA/HHS

Mapped

HCC 67

HHS-HCC 67

Varies by metal level

ESRD/PACE

Mapped

HCC 46

Severe Hematological Disorders

RAF 0.223

RXHCC

Mapped

HCC 19

Lymphoma and Other Cancers

RAF 1.949

Code Book Path

Official

D46Myelodysplastic syndromes

D46.2Refractory anemia with excess of blasts [RAEB]

D46.21Refractory anemia with excess of blasts 1

Inclusion Terms

Official

RAEB 1

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for D46.21 in this effective period.

Related Child Codes

Official

D46.20Refractory anemia with excess of blasts, unspecified

D46.22Refractory anemia with excess of blasts 2

Includes

Official

ICD-10-CM does not list Includes notes for D46.21 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for D46.21 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for D46.21 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for D46.21 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for D46.21 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation must include bone marrow biopsy confirming blast percentage between 5-9%, along with cytogenetic analysis and International Prognostic Scoring System score.

Document peripheral blood counts, transfusion requirements, and any treatment with hypomethylating agents or other therapies.

The specific blast percentage must be explicitly stated in pathology.

MEAT Support

HCC Buddy guidance

Documentation must include bone marrow biopsy confirming blast percentage between 5-9%, along with cytogenetic analysis and International Prognostic Scoring System score.

Document peripheral blood counts, transfusion requirements, and any treatment with hypomethylating agents or other therapies.

The specific blast percentage must be explicitly stated in pathology.

Audit Caution

HCC Buddy guidance

The distinction between RAEB-1 (5-9% blasts) and RAEB-2 (10-19% blasts) is critical for prognosis and treatment decisions.

Verify the exact blast percentage from the pathology report rather than relying on clinical notes alone.

Serial bone marrow biopsies may show blast count progression, requiring code updates over time.

Common Mistakes

HCC Buddy guidance

D46.22 (RAEB-2, 10-19% blasts) indicates a higher blast count with worse prognosis.

D46.20 (excess blasts, unspecified) should not be used when the blast percentage is documented.

D46.0 (refractory anemia without ring sideroblasts) has a lower blast count.

C92.00 (acute myeloblastic leukemia) is used when blasts reach 20%.

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 D46.21 an HCC code?

Yes. D46.21 (Refractory anemia with excess of blasts 1) maps to Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers under the CMS-HCC V28 risk adjustment model (and Severe Hematological Disorders under V24), with a community non-dual aged RAF of 1.798. It is billable for payment year 2026.

Coder answer: D46.21 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: D46.21
Description: Refractory anemia with excess of blasts 1
HCC (V28): HCC 19 — Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers
RAF: 1.798
Billable: Yes
Payment year: 2026

HCC Category Mapping

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

1.798

V24HCC 46, Severe Hematological Disorders

1.372

ESRDHCC 46, Severe Hematological Disorders

0.223

RxHCCHCC 19, Lymphoma and Other Cancers

1.949

Each model's RAF is its CMS base weight for that model's standard population, so 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 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.

Work D46.21 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for D46.21

For D46.21 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 D46.21 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

D46.21 is the ICD-10-CM diagnosis code for refractory anemia with excess of blasts 1. A bone marrow disorder where red blood cells cannot be produced normally and there is an excess of immature blood cells at 5-9% of the bone marrow. D46.21 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering neoplasms of uncertain behavior, polycythemia vera and myelodysplastic syndromes (d37-d48).

Under the CMS-HCC V28 risk adjustment model, D46.21 maps to Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers (HCC 19) with a community, non-dual, aged base RAF weight of 1.798. Under the older CMS-HCC V24 model, D46.21 maps to Severe Hematological Disorders (HCC 46) with a community, non-dual, aged base RAF weight of 1.372. 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.

Requires documentation of blast percentage between 5-9%. Because D46.21 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 D46.21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Requires documentation of blast percentage between 5-9%
•Distinguish from D46.22 which indicates 10-19% blasts

Clinical Significance

Refractory anemia with excess of blasts 1 (RAEB-1) is a higher-risk myelodysplastic syndrome subtype with 5-9% blasts in the bone marrow. This condition carries an intermediate risk of progressing to acute myeloid leukemia, with a median survival of approximately 18-25 months, and typically requires close hematologic surveillance and possibly disease-modifying therapy.

Documentation Requirements

✓Documentation must include bone marrow biopsy confirming blast percentage between 5-9%, along with cytogenetic analysis and International Prognostic Scoring System score.
✓Document peripheral blood counts, transfusion requirements, and any treatment with hypomethylating agents or other therapies.
✓The specific blast percentage must be explicitly stated in pathology.

Commonly Confused Codes

•D46.22 (RAEB-2, 10-19% blasts) indicates a higher blast count with worse prognosis.
•D46.20 (excess blasts, unspecified) should not be used when the blast percentage is documented.
•D46.0 (refractory anemia without ring sideroblasts) has a lower blast count.
•C92.00 (acute myeloblastic leukemia) is used when blasts reach 20%.