A medical student sustains a needlestick injury from an HIV-positive patient and is counselled about post-exposure testing of the source. Which diagnostic assay detects HIV infection at the earliest time point after exposure?

• A Rapid third-generation HIV antibody test
• B Fourth-generation laboratory HIV-1/2 antigen-antibody combination immunoassay ✓
• C Western blot confirmation assay
• D CD4 lymphocyte count with viral load correlation

Explanation

Fourth-generation combination assays detect both p24 antigen and anti-HIV antibodies, closing the diagnostic gap of the purely serological 'window period'. The p24 component becomes positive roughly a week earlier than antibody alone, so the combined assay detects infection around 2 to 3 weeks after exposure, compared with 3 to 8 weeks for third-generation antibody tests. Western blot is a confirmatory test that requires prior antibody positivity, so it cannot be the earliest detector.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.