Which CD4+ T cell count threshold defines AIDS in an HIV-positive patient without any opportunistic infection?

Explanation

## CD4+ Count and AIDS Definition **Key Point:** According to the CDC and WHO classification, AIDS is defined as CD4+ T cell count < 200 cells/μL in an HIV-infected person, regardless of the presence of opportunistic infections. ### CD4+ Count Thresholds and Clinical Significance | CD4+ Count (cells/μL) | Clinical Significance | OI Risk | |---|---|---| | > 500 | Relatively preserved immunity | Minimal | | 200–500 | Moderate immunosuppression | Moderate risk of TB, bacterial infections | | < 200 | Severe immunosuppression | **AIDS-defining threshold** | | < 100 | Very severe | PCP, toxoplasmosis risk | | < 50 | Profound immunosuppression | CMV, MAC risk | **High-Yield:** A CD4+ count < 200 cells/μL is sufficient to diagnose AIDS even in the *absence* of any opportunistic infection or AIDS-defining illness. This is a pure immunological criterion. **Clinical Pearl:** The CD4+ count guides prophylaxis decisions: - < 200 cells/μL → PCP prophylaxis (TMP-SMX) - < 100 cells/μL → Toxoplasmosis prophylaxis - < 50 cells/μL → MAC prophylaxis (azithromycin) [cite:Harrison 21e Ch 197]