Infection / Serology
HIV Ag/Ab combination (4th generation)
Detects p24 antigen + antibodies; window period ~2–4 weeks.
Sample
Serum
Biology
What it measures
Combined detection of HIV-1 p24 antigen and anti-HIV-1/2 antibodies on a single platform.
Clinical use
Why we order it
Universal screening 13–64 y at least once; risk-based repeat testing. Reactive → HIV-1/2 differentiation immunoassay.
Pitfalls
Pre-analytic & interpretation traps
- !Acute (Fiebig stage I–II) HIV may be antibody-negative — order HIV RNA when seroconversion illness is suspected.