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The first tests for HIV antibodies were introduced in 1985 to screen donated blood. Since then, their use has been expanded to include evaluating persons at risk of HIV infection. The two standard HIV tests are the Enzyme Immunoassay (EIA) (also known as the Enzyme-linked Immunosorbent Assay (ELISA)) and the Western Blot (WB).

The EIA/ELISA detects antibodies produced in response to HIV infection. Although some people refer to this initial reaction as a positive result, it should not be considered positive until confirmed with a second, more specific antibody test known as the Western Blot test.

This more specific second test can differentiate between HIV antibodies and other antibodies that react to the EIA, causing positive results even when the person is not actually infected with HIV. However, false-positive EIA results are uncommon.

If your HIV antibody test is negative, you are either uninfected or in the early stages of infection before your body produces HIV antibodies. It can take up to six months—longer, in rare cases—for the body to produce detectable amounts of HIV antibodies. This early period is called seroconversion. Some refer to this time as the "window period" since it offers a window of opportunity for people to unknowingly infect others.

In some cases, an HIV antibody test result is indeterminate or equivocal, meaning HIV antibodies have not yet fully developed. If an indeterminate reading continues for six months or longer, you are considered uninfected.

Rapid antibody tests that produce results within a half hour are now available. In late 2002, the FDA approved the OraQuick rapid test, a blood test that can be read in 20 minutes. Like other HIV tests, the results should be confirmed with other tests.

Another rapid HIV test licensed for use in the U.S. is the Single Use Diagnostic System for HIV-1 (SUDS). The SUDS test requires serum or plasma instead of whole blood obtained from a fingerstick for analysis, more steps and refrigeration.

In 2003, the FDA approved the Uni-Gold Recombigen rapid HIV test, the only test that can be used to test plasma, serum or whole blood. It takes about 10 minutes to obtain results.

An effective alternative to blood testing is an oral fluids test called OraSure, an HIV antibody testing system that uses a cotton pad placed in the mouth to collect oral secretions. The specimen is then sent to a laboratory for analysis. The test, available only in clinics or health care professionals' offices, is as accurate as a blood test and costs about the same as a blood test. As with both rapid tests, positive OraSure tests should be confirmed with standard HIV testing.

An over-the-counter HIV test that you can perform in your home is also available. Although there are several home tests advertised, only one, Home Access Express HIV-1 Test System, is approved by the FDA. The Home Access test uses a simple finger prick process for collecting blood. You place the specimen on special paper and mail it to a laboratory. Each test comes with a confidential or anonymous personal identification number. You receive test results by making a toll-free call. If this type of test interests you, ask your health care professional for more information about where to purchase it and how to use it correctly.

There is now an HIV urine test available for use in the health care professional's office, but it's less accurate than standard blood tests. There are also two viral tests for HIV that measure the amount of virus in the blood directly: the p24 antigen test and the RNA viral load test. The p24 antigen test measures p24 antigen, a protein that is part of HIV and shows up two to three weeks after infection.