Human Immunodeficiency Virus (HIV) Test

Test Overview

A human immunodeficiency virus (HIV) test detects HIV antibodies or antigens, or the genetic material (DNA or RNA) of HIV in the blood or another type of sample. This determines whether an HIV infection is present (HIV-positive). HIV infects white blood cells called CD4+ cells, which are part of the body's immune system that help fight infections. HIV can progress to acquired immunodeficiency syndrome (AIDS).

After the original infection, it takes about 4 to 12 weeks for HIV antibodies or antigens to appear in the blood. The period between becoming infected with HIV and the point at which antibodies or antigens to HIV can be detected in the blood is called the seroconversion or "window" period. During this period, an HIV-infected person can still spread the disease, even though a test will not detect any antibodies or antigens in his or her blood.

Several tests can find antibodies to or genetic material (RNA) of the HIV virus. These tests include:

• Enzyme-linked immunosorbent assay (ELISA). This test is usually the first one used to detect infection with HIV. If antibodies to HIV are present (positive), the test is usually repeated to confirm the diagnosis. If ELISA is negative, other tests are not usually needed. This test has a low chance of having a false result after the first few weeks that a person is infected.
• Polymerase chain reaction (PCR). This test finds either the RNA of the HIV virus or the HIV DNA in white blood cells infected with the virus. PCR testing is not done as frequently as antibody testing, because it requires technical skill and expensive equipment. This test may be done in the days or weeks after exposure to the virus. Genetic material may be found even if other tests are negative for the virus. The PCR test is very useful to find a very recent infection, determine if an HIV infection is present when antibody test results were uncertain, and screen blood or organs for HIV before donation.
• Indirect fluorescent antibody (IFA). This test detects HIV antibodies using a special fluorescent dye and a microscope. This test may be used to confirm the results of an ELISA test.

If HIV antibodies or antigens are not found, the test may be repeated in a few months.

If you have a positive test result, contact your sex partners to inform them. They may want to be tested. You may be able to get help from your local health department to do this.

Home test kits

Two types of home test kits for HIV have been approved by the U.S. Food and Drug Administration (FDA). If the results from a home test kit show that you have an HIV infection, talk to a doctor. And keep in mind that these test kits sometimes may show that you have HIV when you don't (false-positive result) or may show that you don't have HIV when you do (false-negative result).

• One test kit (called OraQuick) gives you the results right away. For this test, you rub your gums with a swab supplied by the kit. Then you place the swab into a vial of liquid. The test strip on the swab indicates if you have HIV or not.
• Another type of test kit for HIV is a home blood test kit. This kit provides instructions and materials for collecting a small blood sample by sticking your finger with a lancet. The blood is placed onto a special card that is then sent to a lab for analysis. You can find out your results over the phone by using an anonymous code number. Counseling is also available over the phone for people who use the test kit.