The DNA test for HIV infection can detect the presence of the virus in the body much earlier than the standard test, usually around 7-10 days after infection. Here's how the two tests work.

Shortly after a person becomes infected with HIV, the body begins to make antibodies that specifically recognize HIV. Antibodies are proteins that try to fight off an infection. Each kind of antibody recognizes only the infection it is designed to fight.

In the case of HIV infection, these antibodies are not effective at fighting the virus. But, because they appear only after a person has been infected with HIV, their detection is useful as a diagnostic test. The HIV antibody test (also known as an ELISA or EIA) is the standard HIV test. The test doesn't look for the virus directly. Rather, it looks for the body's response to the virus, in the form of antibodies. It's an accurate test, but it can take 3 weeks to 6 months after infection for the body to produce a detectable amount of HIV-specific antibodies.

The DNA test (properly known as NAAT, for Nucleic Acid Amplification Testing) looks for HIV directly, and can detect its presence much earlier than the antibody test. (This test is very similar to the viral load test used to monitor whether an HIV-infected patient's medications are controlling the virus.)

There are several drawbacks to NAAT testing as a technique for detecting HIV infection, however. One is that it is actually too sensitive, meaning that it will sometimes give a positive result even though a person hasn't been infected. This can be upsetting. For this reason, any positive NAAT test needs to be followed up by a series of standard antibody tests to confirm that a patient is either infected or uninfected. Another drawback is that it is not widely offered as a test for detecting HIV, although some doctors will sometimes use a viral load test for this purpose.