D66
BillableHereditary factor VIII deficiency
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is D66 an HCC code?
Yes. D66 maps to Hemophilia, Male under the CMS-HCC V28 risk adjustment model (and Severe Hematological Disorders under V24).
HCC Category Mapping
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 D66
For D66to 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 D66 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
D66 is the ICD-10-CM diagnosis code for hereditary factor viii deficiency. A hereditary bleeding disorder caused by deficiency or dysfunction of clotting factor VIII, commonly known as hemophilia A. D66 sits in the ICD-10-CM chapter for diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism (d50-d89), within the section covering coagulation defects, purpura and other hemorrhagic conditions (d65-d69).
Under the CMS-HCC V28 risk adjustment model, D66 maps to Hemophilia, Male (HCC 111) with a community, non-dual, aged base RAF weight of 4.639. Under the older CMS-HCC V24 model, D66 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.
Specify the severity level (mild, moderate, severe) if documented. Because D66 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 D66 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Specify the severity level (mild, moderate, severe) if documented
- •Use additional codes for any complications such as inhibitor development
Clinical Significance
Hereditary factor VIII deficiency (Hemophilia A) is the most common severe inherited bleeding disorder, caused by deficient or defective clotting factor VIII. Severity correlates with factor VIII activity levels: severe (<1%), moderate (1-5%), or mild (5-40%). This condition requires lifelong factor replacement therapy and carries significant healthcare resource utilization with a high RAF weight.
Documentation Requirements
- ✓Document the severity level (severe, moderate, mild) based on factor VIII activity levels.
- ✓Record current treatment regimen including factor replacement products, dosing frequency, and whether the patient has developed inhibitors (antibodies to factor VIII).
- ✓Note any target joints, history of intracranial hemorrhage, and hepatitis/HIV status if applicable from prior blood product exposure.
Excludes 1 — Do NOT code together
- factor VIII deficiency with vascular defect (D68.0-)
Commonly Confused Codes
- •D67 (Hereditary factor IX deficiency/Hemophilia B) — clinically similar but different factor deficiency requiring different replacement products
- •D68.311 (Acquired hemophilia) — autoimmune condition developing later in life with autoantibodies against factor VIII
- •D68.00-D68.09 (Von Willebrand disease) — may have low factor VIII but primary defect is in von Willebrand factor.