D81.31
BillableSevere combined immunodeficiency due to adenosine deaminase deficiency
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is D81.31 an HCC code?
Yes. D81.31 maps to Severe Combined Immunodeficiency and Other Immune Disorders under the CMS-HCC V28 risk adjustment model (and Disorders of Immunity 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 D81.31
For D81.31to 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 D81.31 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
D81.31 is the ICD-10-CM diagnosis code for severe combined immunodeficiency due to adenosine deaminase deficiency. A severe inherited immune deficiency caused by lack of the enzyme adenosine deaminase, resulting in inability to fight infections. D81.31 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 certain disorders involving the immune mechanism (d80-d89).
Under the CMS-HCC V28 risk adjustment model, D81.31 maps to Severe Combined Immunodeficiency and Other Immune Disorders (HCC 114) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, D81.31 maps to Disorders of Immunity (HCC 47) with a community, non-dual, aged base RAF weight of 0.472. 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.
Confirm adenosine deaminase enzyme levels are documented as deficient. Because D81.31 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 D81.31 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Confirm adenosine deaminase enzyme levels are documented as deficient
- •Verify SCID diagnosis is confirmed through immunological testing showing absent T-cells and B-cells
Clinical Significance
Severe combined immunodeficiency due to adenosine deaminase deficiency accounts for approximately 15% of all SCID cases and results from toxic accumulation of deoxyadenosine and its metabolites, which selectively destroy lymphocytes. Unlike other SCID forms, adenosine deaminase-SCID also affects non-immune tissues including skeletal, hepatic, and neurological systems, making it a systemic metabolic disease as well as an immunodeficiency.
Documentation Requirements
- ✓Documentation must include confirmed adenosine deaminase enzyme deficiency through activity assay, elevated deoxyadenosine triphosphate levels in red blood cells, lymphocyte subset analysis showing profoundly reduced T-cells, B-cells, and natural killer cells, and treatment modality (enzyme replacement with pegademase, hematopoietic stem cell transplant, or gene therapy).
- ✓Document skeletal and neurological assessments.
Commonly Confused Codes
- •D81.30 (adenosine deaminase deficiency, unspecified, which lacks SCID confirmation), D81.39 (other adenosine deaminase deficiency for partial or delayed forms), D81.32 (adenosine deaminase 2 deficiency, a completely different condition), D81.1 (severe combined immunodeficiency with low T
- •and B-cells from other causes), D81.5 (purine nucleoside phosphorylase deficiency).