An advanced fourth-generation immunoassay for HIV. It simultaneously detects the viral p24 antigen (a capsid protein that appears early in the blood after infection) and antibodies (IgG and IgM) directed against the virus. This combination significantly reduces the immune window (the time between infection and detection) to approximately 14–28 days, compared to 3–6 weeks for antibody-only tests. It is now the internationally recommended initial screening test for HIV.