Final answer:
After HIV exposure, viral RNA levels rise before antibodies are detectable. Nucleic acid tests can detect viral RNA, whereas antibodies may take several weeks to months to develop.
Step-by-step explanation:
When exposed to HIV, the viral RNA levels rise first, which can be detected by nucleic acid tests (NATs). After infection, it usually takes a while for the body to produce antibodies (HIV Abs) against the virus. Early in the disease, the increase in anti-HIV antibodies correlates with a decrease in detectable virus in the blood, which is known as seroconversion.
However, these antibodies cannot fully control the virus. The fourth-generation tests can detect both HIV antigens and antibodies, but if someone seeks to diagnose HIV infection immediately after exposure, tests that identify viral RNA are the most useful as they can detect the virus before antibodies develop.