HIV-1/2 Antigen-Antibody Combination (4th Generation)
This blood test, known as a fourth-generation or antigen-antibody combination test, looks for two things at once: a viral protein called p24 antigen and antibodies to HIV-1 and HIV-2. Together they help detect HIV infection.
Because it detects the p24 antigen, which appears soon after infection, this test can identify HIV earlier than tests that look for antibodies alone. Detecting HIV allows people to start effective treatment, which protects long-term health and greatly reduces the chance of passing the virus to others. It is a widely recommended, standard screening test.
A positive (reactive) result suggests HIV infection, but it is considered a preliminary result that always requires confirmatory testing before a diagnosis is made. Follow-up tests are used to confirm the result and to determine whether the infection is HIV-1 or HIV-2. Your clinician will explain the next steps; a reactive screening test on its own is not a final diagnosis.
A negative (non-reactive) result means no HIV antigen or antibodies were detected, which generally means you are not infected. However, there is a window period soon after exposure when the test may not yet detect an early infection, so repeat testing may be recommended if you had a possible exposure within the preceding weeks.
The expected, normal result is negative (non-reactive). If you have had a recent possible exposure, your clinician may recommend repeat testing after the window period to be confident in the result, and any reactive result is confirmed with additional testing before a diagnosis.
Sources
Educational context only, not medical advice or a diagnosis. Reference ranges vary by lab, age and sex; always discuss your results with a clinician.