Exams and Tests

HIV infection is commonly diagnosed by blood tests that detect antibodies the body makes in an attempt to fight the virus. It can take some time for the immune system to produce enough antibodies for the antibody test to detect them. This time period is commonly referred to as the "window period" and may take six weeks to three months following infection. Therefore, if the initial test after exposure is negative, a repeat test should be performed three months later. Early testing is crucial, because early treatment for HIV helps people avoid or minimize complications. Furthermore, high-risk behaviors can be avoided, thus preventing the spread of the virus to others.

Testing for HIV is a two-step process. First, an inexpensive screening test is done. If that test is positive, a second test (Western blot) is done to confirm the result.

• There are different types of screening tests available in the United States. The enzyme immunoassay (EIA) used on the blood is the most common screening test. Other EIA tests can detect antibodies in body fluids other than blood such as oral fluid, urine, and vaginal secretions.



• Rapid tests are alternative screening tests that produce quick results in approximately 20 minutes. There are FDA-approved tests that use blood or oral fluid. These tests have accuracy rates similar to traditional EIA tests.



• HIV home-testing kits are available at many local drug stores. Blood is obtained by a finger prick and blotted on a filter strip. The blood is mailed in a protective envelope to a laboratory to be tested.



• All positive screening tests must be confirmed with a follow-up blood test called the Western blot to make a positive diagnosis.

Other tests, such as those that look for virus RNA, are used less commonly.