The EIA (enzyme immunoassay) is the standard screening test used to detect the presence of antibodies to HIV. The EIA should be used with a confirmatory test such as the Western Blot. Tests that detect other signs of HIV are available for special purposes, such as for additional testing of the blood supply and conducting research. Because some tests are expensive or require sophisticated equipment and specialized training, their use is limited.

In addition to the EIA, other tests now available include:
• Radioimmunoprecipitation assay (RIPA): A confirmatory blood test that may be used when antibody levels are very low or difficult to detect or when Western blot test results are uncertain. An expensive test, the RIPA requires time and expertise to perform.
• Rapid latex agglutination assay: A simplified, inexpensive blood test that may prove useful in medically disadvantaged areas where there is a high prevalence of HIV infection.
• Dot-blot immunobinding assay: A rapid-screening blood test that is cost-effective and that may become an alternative to conventional EIA and Western Blot testing.
• p24 antigen capture assay: Also known as the HIV-1 antigen capture assay. This blood test was added as an interim measure by the Food and Drug Administration (FDA) in 1996 to HIV-antibody testing to protect the blood supply further until other tests become available to detect early HIV infection before antibodies are fully developed. Because some activity of p24 antigen is unpredictable, this test is not useful for helping people find out if they have HIV.
• Polymerase chain reaction (PCR): A specialized blood test that looks for HIV genetic information. Although expensive and labor-intensive, the test can detect the virus even in someone only recently infected. To further protect the blood supply, the FDA has indicated that the development and implementation of tests for HIV genetic material such as PCR is warranted.