HIV/AIDS: Screening and Diagnosis

HIV is usually diagnosed by testing your blood for the presence of antibodies to the virus. Unfortunately, many HIV tests aren't accurate immediately after infection because it takes time for your body to develop these antibodies — usually from six to 12 weeks. In rare cases it can take up to six months for an HIV test to become positive. If you're suspected of having HIV, however, special tests are available that can diagnose infection before antibodies develop.

For years, the only available test for HIV was the enzyme-linked immunosorbent assay (ELISA) test that looked for antibodies to the virus in a sample of your blood. If this test was positive — meaning you had antibodies to HIV — the same test was repeated. If the repeat test was also positive for HIV antibodies, you'd then have another confirming blood test called the Western blot test, which checks for the presence of HIV proteins. The Western blot test was important because you may have non-HIV antibodies that cause a false-positive result on the ELISA test. Combining the two types of tests helped ensure that the results were accurate, and you'd receive a diagnosis of HIV only if all three tests were positive.

The downside is that it can take up to two weeks to get the results of the ELISA and Western blot tests, a period of time that can take an emotional toll and that discourages many people from returning to get their test results. Now, however, two "rapid" tests can give highly accurate information within as little as 20 minutes.

Both rapid tests look for antibodies to the virus, but one uses a sample of your blood and requires a finger prick. The other relies on fluids collected on a treated pad that's rubbed on your upper and lower gums. The oral test is almost as sensitive as the blood test and eliminates the need for drawing blood.

Keep in mind that a positive reaction on either test requires a confirming blood test. And because the tests are relatively new and were originally approved for use only in certified laboratories, they may not be available in all locations.