How HIV is diagnosed

As the body fights a particular virus, it creates substances called antibodies to that virus. Tests for HIV usually measure the presence of HIV antibodies in blood, urine, or saliva, rather than testing for the presence of HIV itself (San Francisco AIDS Foundation [SFAF], 1998a).

Main types of HIV tests

Several different types of tests can be used to detect HIV. An Enzyme-Linked Immunosorbent Assay (ELISA) determines HIV antibodies' presence in blood or oral fluids. When people show HIV antibodies on two or more ELISA tests, they undergo an independent, highly specific supplemental test (most commonly, the Western Blot test) to confirm ELISA's results (Constantine, n.d.). Western Blot is a highly specific supplemental test that detects the presence of HIV antibodies in the blood. The Western Blot test is less sensitive than the ELISA test, but it hardly ever gives a false positive result; therefore, it is used for confirming the ELISA test. Rapid serum HIV antibody tests, saliva- and urine-based antibody tests, and home HIV antibody testing kits also have been approved by the Food and Drug Administration (FDA) and are commercially available (Constantine, n.d.). The rapid HIV tests can be administered outside of a traditional laboratory setting and processed in as little as 20 minutes (CDC, 2003b, 2006). HIV RNA tests are being used in research and healthcare settings to diagnose HIV infection very early after exposure, before antibodies are even formed (Constantine, n.d.). These tests look for bits of HIV RNA in the blood.