D84.821 ICD-10-CM Code: Immunodeficiency due to drugs
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)
D84.821
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceImmunodeficiency due to drugs
A weakened immune system caused by medications the patient is taking, such as chemotherapy, immunosuppressants, or corticosteroids.
Buddy Insight
Immunodeficiency due to drugs represents iatrogenic immunosuppression caused by medications including chemotherapy agents, corticosteroids, disease-modifying antirheumatic drugs, calcineurin inhibitors, and biologic agents such as anti-tumor necrosis factor therapies and rituximab.
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
Official- Immunodeficiency due to (current or past) medication
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for D84.821 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for D84.821 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for D84.821 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for D84.821 in this effective period.
Use Additional
Official- code for adverse effect if applicable, to identify adverse effect of drug (T36-T50 with fifth or six character 5)
Code Also
OfficialICD-10-CM does not list Code Also instructions for D84.821 in this effective period.
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 D84.821 an HCC code?
Yes. D84.821 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.
MEAT Criteria for D84.821
For D84.821to 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 D84.821 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
D84.821 is the ICD-10-CM diagnosis code for immunodeficiency due to drugs. A weakened immune system caused by medications the patient is taking, such as chemotherapy, immunosuppressants, or corticosteroids. D84.821 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, D84.821 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.
Document the specific medication causing the immunodeficiency in the medical record. Because D84.821 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 D84.821 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Document the specific medication causing the immunodeficiency in the medical record
- •Code the underlying condition being treated with the immunosuppressive medication as well
Clinical Significance
Immunodeficiency due to drugs represents iatrogenic immunosuppression caused by medications including chemotherapy agents, corticosteroids, disease-modifying antirheumatic drugs, calcineurin inhibitors, and biologic agents such as anti-tumor necrosis factor therapies and rituximab. This condition reflects the increased infection risk and immune dysfunction that occurs as a direct consequence of pharmacological treatment.
Documentation Requirements
- ✓Documentation must identify the specific medication(s) causing immunodeficiency, the underlying condition being treated, evidence of immune impairment (opportunistic infections, low immunoglobulin levels, lymphopenia), and whether the immunosuppression is intentional (transplant rejection prevention) or an adverse effect.
- ✓Include appropriate adverse effect or long-term medication use codes (T-codes or Z-codes).
Use Additional Code
Commonly Confused Codes
- •D84.81 (immunodeficiency due to conditions classified elsewhere, which is disease-related not drug-related), D84.822 (immunodeficiency due to external causes like radiation), Z79.899 (long-term use of other medications without documented immunodeficiency), T45.1X5A (adverse effect of antineoplastic drugs, which captures the drug reaction but not the immune deficit).