What is ICD-10 code D81.31?

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 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. D81.31 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. D81.31 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. D81.31 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 D81.31?

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 D81.31, V28 maps to Severe Combined Immunodeficiency and Other Immune Disorders at RAF 0.000 while V24 mapped to Disorders of Immunity at RAF 0.472. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting D81.31?

Confirm adenosine deaminase enzyme levels are documented as deficient Verify SCID diagnosis is confirmed through immunological testing showing absent T-cells and B-cells Because D81.31 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.

D81.31 ICD-10 Code: Severe combined

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 lookupD81.31Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism (D50-D89) / Certain disorders involving the immune mechanism (D80-D89)

D81.31

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

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.

Buddy Insight

CMS-HCC V28

Mapped

HCC 114

Severe Combined Immunodeficie...

RAF 0.0

CMS-HCC V24

Mapped

HCC 47

Disorders of Immunity

RAF 0.472

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 47

Disorders of Immunity

RAF 0.0

RXHCC

Mapped

HCC 99

Immunodeficiencies

RAF 0.0

Code Trumping

Basket needed

Compare selected patient codes to show trumped or trumps impact.

Code Book Path

Official

D81Combined immunodeficiencies

D81.3Adenosine deaminase [ADA] deficiency

D81.31Severe combined immunodeficiency due to adenosine deaminase deficiency

Inclusion Terms

Official

ADA deficiency with SCID
Adenosine deaminase [ADA] deficiency with severe combined immunodeficiency

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for D81.31 in this effective period.

Related Child Codes

Official

D81.30Adenosine deaminase deficiency, unspecified

D81.32Adenosine deaminase 2 deficiency

D81.39Other adenosine deaminase deficiency

Includes

Official

ICD-10-CM does not list Includes notes for D81.31 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for D81.31 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for D81.31 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for D81.31 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for D81.31 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

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.

MEAT Support

HCC Buddy guidance

Document skeletal and neurological assessments.

Audit Caution

HCC Buddy guidance

Ensure documentation confirms both the adenosine deaminase enzyme deficiency AND the SCID phenotype; partial adenosine deaminase deficiency with mild immune impairment should be coded as D81.

Do not confuse with adenosine deaminase 2 deficiency (D81.32), which presents with vasculitis rather than immunodeficiency. The availability of enzyme replacement therapy (pegademase bovine) is specific to this condition.

Common Mistakes

HCC Buddy guidance

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).

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 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

V28HCC 114, Severe Combined Immunodeficiency and Other Immune Disorders

0.000

V24HCC 47, Disorders of Immunity

0.472

ESRDHCC 47, Disorders of Immunity

0.000

RxHCCHCC 99, Immunodeficiencies

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 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).