Z21
BillableAsymptomatic human immunodeficiency virus [HIV] infection status
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is Z21 an HCC code?
Yes. Z21 maps to HIV/AIDS under the CMS-HCC V28 risk adjustment model (and HIV/AIDS 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 Z21
For Z21to 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 Z21 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
Z21 is the ICD-10-CM diagnosis code for asymptomatic human immunodeficiency virus [hiv] infection status. A person who has tested positive for HIV but has not yet developed AIDS or shown symptoms of HIV infection. Z21 sits in the ICD-10-CM chapter for factors influencing health status and contact with health services (z00-z99), within the section covering persons with potential health hazards related to communicable diseases (z20-z29).
Under the CMS-HCC V28 risk adjustment model, Z21 maps to HIV/AIDS (HCC 1) with a community, non-dual, aged base RAF weight of 0.309. Under the older V24 model, Z21 mapped to the same category but with a base RAF weight of 0.311 — V28 recalibrated weights across the entire model. 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.
This code indicates asymptomatic HIV status; if the patient develops AIDS or symptomatic disease, use B20 codes instead. Because Z21 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 Z21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code indicates asymptomatic HIV status; if the patient develops AIDS or symptomatic disease, use B20 codes instead
- •Document the patient's CD4 count and viral load status in the medical record for comprehensive care tracking
Clinical Significance
Asymptomatic HIV infection status indicates ongoing viral infection requiring regular monitoring, antiretroviral therapy, and preventive care to prevent progression to AIDS. This diagnosis represents a chronic condition with significant implications for immune system function and overall health management.
Documentation Requirements
- ✓Laboratory confirmation of HIV-positive status
- ✓Documentation that patient is asymptomatic for HIV disease
- ✓Current CD4 count and viral load results when available
- ✓Antiretroviral therapy regimen if prescribed
- ✓Assessment of HIV disease stage or classification
- ✓Screening for opportunistic infections
- ✓Counseling and education provided
- ✓Plans for ongoing HIV monitoring and care
Excludes 1 — Do NOT code together
Code First
- Human immunodeficiency virus [HIV] disease complicating pregnancy, childbirth and the puerperium, if applicable (O98.7-)
Commonly Confused Codes
- •B20 — Human immunodeficiency virus disease (symptomatic HIV/AIDS)
- •Z87.891 — Personal history of nicotine dependence (different risk factor)
- •Z11.4 — Encounter for screening for human immunodeficiency virus
- •R75 — Inconclusive laboratory evidence of human immunodeficiency virus
- •O98.72 — Human immunodeficiency virus disease complicating pregnancy