Merck Manuals, an online medical library, reports that human immunodeficiency virus (HIV) causes a progressive, chronic infection that kills a type of white blood cell, which are the cells of the immune system. HIV ultimately causes acquired immune deficiency syndrome (AIDS), which makes the body susceptible to many types of infections that usually pose no problem to people with normal immune systems. Several types of laboratory tests exist that measure the presence of virus in bodily tissues.
ELISA
The Body Health Resources Corporation, an online HIV/AIDS resource, reports that the first screening tool to detect HIV infection includes an enzyme-linked immunosorbent assay or ELISA. This test detects the virus indirectly by measuring antibodies made by the body that specifically bind HIV. Antibodies are proteins made by certain cells of the immune system in response to all infections. When the test detects antibodies, this indicates that the person has become infected with HIV. The Body Health Resources Corporation adds that the HIV ELISA can only detect HIV infection 3 to 6 months after infection, because it takes time for antibodies to develop in response to infection. Blood proves the most commonly tested body tissue, but ELISAs can also detect HIV antibodies in saliva and urine. Traditional ELISAs take about 4 hours to complete; a newer rapid HIV ELISA tests can take 10 to 20 minutes to perform. However, a person can wait days or weeks because most tests are performed by outside laboratories.
Western Blot Assay
The western blot (WB) assay confirms the results of an ELISA HIV test, according to the Body Health Resources Corporation. The WB assay tests for the HIV antibodies in a different manner than the ELISA test, and thus provides a way to independently confirm the presence of HIV antibodies. False positive results with the WB assay prove very rare.
Polymerase Chain Reaction (PCR) Test
AIDS.gov, a service provided by the U.S. Department of Health and Human Services, reports that another way to detect HIV infection is the polymerase chain reaction (PCR) test. The PCR test detects the genetic material (DNA) of HIV. One advantage to the PCR test includes its ability to detect the HIV virus much earlier than the ELISA test, at 2 to 3 weeks after infection. The PCR test can also determine the HIV status of a baby born to an HIV-infected mother. Because the blood of a baby contains the mother's antibodies for several months after birth, only a PCR test, which tests for the virus directly, can determine if a baby has indeed become infected with the virus.
