What is ICD-10 code D84.9?

D84.9 is the ICD-10-CM diagnosis code for Immunodeficiency, unspecified. A weakened immune system where the specific cause or type of immune deficiency has not been identified or specified. D84.9 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. D84.9 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. D84.9 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. D84.9 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.

Which HCC does D84.9 map to under V28?

D84.9 does not map to a CMS-HCC V28 payment category. Check the current CMS-HCC V28 model file for payment year 2026 rather than an older V24 tip sheet.

What does D84.9 pay in RAF?

D84.9 has no separately stated V28 community RAF weight. If it is not a V28 payment HCC, it adds nothing to a community RAF score.

What is the V28 vs V24 difference for D84.9?

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. D84.9 was a payment HCC under V24 (Disorders of Immunity) but the V28 recalibration removed it from the risk adjustment model. Both models can still appear in legacy data and in payer-specific lookback periods.

2026 ICD-10-CM D84.9: Immunodeficiency, unspecified

D84.9 is not a CMS-HCC payment code. MEAT criteria · RAF calculator · HCC Buddy coding tools

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 lookupD84.9Effective 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)

D84.9

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

Immunodeficiency, unspecified

A weakened immune system where the specific cause or type of immune deficiency has not been identified or specified.

Buddy Insight

Immunodeficiency, unspecified, indicates that a patient has been diagnosed with a weakened immune system but the specific type, cause, or mechanism has not been determined or documented.

CMS-HCC V28

N/A

—

Not risk-adjusted for this model/period.

Not mapped

CMS-HCC V24

Mapped

HCC 47

Disorders of Immunity

RAF 0.665

ACA/HHS

Mapped

HCC 74

HHS-HCC 74

Varies by metal level

ESRD/PACE

Mapped

HCC 47

Disorders of Immunity

RAF 0.078

RXHCC

Mapped

HCC 99

Immunodeficiencies

RAF 0.943

Code Book Path

Official

D84Other immunodeficiencies

D84.9Immunodeficiency, unspecified

Inclusion Terms

Official

Immunocompromised NOS
Immunodeficient NOS
Immunosuppressed NOS

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for D84.9 in this effective period.

Related Child Codes

Official

D84.0Lymphocyte function antigen-1 [LFA-1] defect

D84.1Defects in the complement system

D84.8Other specified immunodeficiencies

Includes

Official

ICD-10-CM does not list Includes notes for D84.9 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for D84.9 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for D84.9 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for D84.9 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for D84.9 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation should include the clinical basis for diagnosing immunodeficiency (recurrent or unusual infections, laboratory evidence of immune dysfunction), the reason why further specificity cannot be achieved, and the plan for additional diagnostic workup.

Include available immunological test results even if incomplete, and document any empiric treatment provided.

MEAT Support

HCC Buddy guidance

Include available immunological test results even if incomplete, and document any empiric treatment provided.

Audit Caution

HCC Buddy guidance

This is the most audit-vulnerable immunodeficiency code and should only be used when genuinely no further information is available.

Review the medical record thoroughly for immunological testing, specialist consultations, and infection patterns that might support a more specific code.

Provider queries should be initiated whenever this code appears to be the default assignment rather than clinically justified.

Common Mistakes

HCC Buddy guidance

D84.89 (other immunodeficiencies when the type is specified but lacks its own code), D80.9 (unspecified antibody deficiency when humoral defects are identified), D81.9 (combined immunodeficiency, unspecified, when both cellular and humoral defects are documented), D83.9 (common variable immunodeficiency, unspecified, which requires meeting CVID diagnostic criteria).

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 D84.9 an HCC code?

Yes. D84.9 maps to Disorders of Immunity under the V24 model but is not retained in V28.

Code: D84.9
Description: Immunodeficiency, unspecified
HCC (V28): No CMS-HCC V28 mapping
RAF: —
Billable: Yes
Payment year: 2026

HCC Category Mapping

V24HCC 47, Disorders of Immunity

0.665

ESRDHCC 47, Disorders of Immunity

0.078

RxHCCHCC 99, Immunodeficiencies

0.943

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 D84.9 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for D84.9

For D84.9 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 D84.9 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

D84.9 is the ICD-10-CM diagnosis code for immunodeficiency, unspecified. A weakened immune system where the specific cause or type of immune deficiency has not been identified or specified. D84.9 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 older CMS-HCC V24 model, D84.9 maps to Disorders of Immunity (HCC 47) with a community, non-dual, aged base RAF weight of 0.665. 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.

Use only when the type of immunodeficiency cannot be determined from documentation. Because D84.9 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 D84.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Use only when the type of immunodeficiency cannot be determined from documentation
•Encourage providers to specify the type of deficiency for more accurate coding

Clinical Significance

Immunodeficiency, unspecified, indicates that a patient has been diagnosed with a weakened immune system but the specific type, cause, or mechanism has not been determined or documented. This code represents the broadest and least specific immunodeficiency diagnosis, often assigned during initial evaluation before a definitive immunological workup is complete.

Documentation Requirements

✓Documentation should include the clinical basis for diagnosing immunodeficiency (recurrent or unusual infections, laboratory evidence of immune dysfunction), the reason why further specificity cannot be achieved, and the plan for additional diagnostic workup.
✓Include available immunological test results even if incomplete, and document any empiric treatment provided.

Commonly Confused Codes

•D84.89 (other immunodeficiencies when the type is specified but lacks its own code), D80.9 (unspecified antibody deficiency when humoral defects are identified), D81.9 (combined immunodeficiency, unspecified, when both cellular and humoral defects are documented), D83.9 (common variable immunodeficiency, unspecified, which requires meeting CVID diagnostic criteria).