HIV Test: 4th Generation Antigen/Antibody Screen with Reflexes

The screening step measures HIV-1 p24 antigen together with antibodies to HIV-1 and HIV-2 in a single immunoassay. If that screen is reactive, Quest's algorithm adds an antibody differentiation test that looks separately for HIV-1 and HIV-2 antibodies. If the differentiation result is negative or indeterminate, a qualitative real-time PCR test checks the sample for HIV-1 and HIV-2 RNA. The report ends with an overall HIV interpretation that combines every step that was performed.

Anyone who has never been tested: the CDC recommends at least one HIV test for everyone aged 13 to 64, and the USPSTF recommends screening for adolescents and adults aged 15 to 65 and for all pregnant people. People with ongoing risk, such as having had more than one sex partner since the last test, sharing injection equipment, or exchanging sex for money or drugs, should test at least yearly, and sexually active gay and bisexual men may benefit from testing every 3 to 6 months. It also suits anyone who wants to check after a possible exposure, after a new partner, or alongside other STI screening.

Any time for routine screening; no fasting or preparation is needed. After a specific possible exposure, timing matters: a lab antigen/antibody test can usually detect HIV 18 to 45 days after exposure, so a negative result earlier than that is not conclusive. CDC advises retesting after the window period if you test negative after a possible exposure. If you think you were exposed within the last 72 hours, contact a clinician or urgent care right away about post-exposure prophylaxis (PEP) instead of waiting to test.

A non-reactive result means neither HIV antigen nor HIV antibodies were detected. If you were tested at least 45 days after your last possible exposure, that generally means you do not have HIV; if the test was earlier, retest after the window period. A reactive screen is not a diagnosis by itself: Quest automatically performs an antibody differentiation test, and if needed an HIV RNA test, on the same sample. The final interpretation on your report states whether HIV-1 or HIV-2 infection is confirmed, not confirmed, or whether more testing is recommended. A confirmed positive result means you should see a clinician promptly to start care; the CDC recommends starting HIV treatment as soon as possible after diagnosis. JustLabs results are informational, so review any reactive or unclear result with a clinician.