D84.822 ICD-10-CM Code: Immunodeficiency due to external causes
HCC Buddy Code Card
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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)
D84.822
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceImmunodeficiency due to external causes
A weakened immune system caused by external factors such as radiation therapy, severe malnutrition, or environmental exposure.
Buddy Insight
Immunodeficiency due to external causes represents immune system compromise resulting from environmental or external exposures such as ionizing radiation, severe malnutrition, or toxic chemical exposure.
CMS-HCC V28
00
RAF 0
CMS-HCC V24
MappedHCC 47
RAF 0.472
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 47
RAF 0.0
RXHCC
MappedHCC 99
RAF 0.0
Code Trumping
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Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for D84.822 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for D84.822 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for D84.822 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for D84.822 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for D84.822 in this effective period.
Use Additional
Official- code for external cause such as:
- exposure to ionizing radiation (W88)
Code Also
Official- , if applicable, radiological procedure and radiotherapy (Y84.2)
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 D84.822 an HCC code?
Yes. D84.822 maps to Disorders of Immunity under the V24 model but is not retained in V28.
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.
Work D84.822 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for D84.822
For D84.822to 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 D84.822 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
D84.822 is the ICD-10-CM diagnosis code for immunodeficiency due to external causes. A weakened immune system caused by external factors such as radiation therapy, severe malnutrition, or environmental exposure. D84.822 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, D84.822 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.
Identify and document the specific external cause (radiation, malnutrition, etc.). Because D84.822 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 D84.822 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Identify and document the specific external cause (radiation, malnutrition, etc.)
- •May require an external cause code (Chapter 20) depending on the circumstances
Clinical Significance
Immunodeficiency due to external causes represents immune system compromise resulting from environmental or external exposures such as ionizing radiation, severe malnutrition, or toxic chemical exposure. These external factors damage immune cell populations or impair immune function through mechanisms distinct from genetic immunodeficiency or drug-induced immunosuppression.
Documentation Requirements
- ✓Documentation must identify the specific external cause of immunodeficiency (radiation exposure type and dose, nutritional deficiency specifics, toxic exposure), include evidence of resulting immune dysfunction (lymphopenia, recurrent infections, impaired vaccine responses), and describe the temporal relationship between the external exposure and immune impairment.
- ✓Assign appropriate external cause codes from Chapter 20.
Use Additional Code
- code for external cause such as:
- exposure to ionizing radiation (W88)
Code Also
- , if applicable, radiological procedure and radiotherapy (Y84.2)
Commonly Confused Codes
- •D84.821 (immunodeficiency due to drugs, which is pharmaceutical rather than environmental), D84.81 (immunodeficiency due to conditions classified elsewhere, which is disease-related), E46 (unspecified protein-calorie malnutrition which may cause immunodeficiency but should be coded primarily with D84.822 as additional), D84.9 (immunodeficiency, unspecified, which does not identify the external cause).