HIV Antibody Test
In the early stages of HIV infection, the virus itself is difficult to detect. Rather than looking for the virus, HIV testing usually involves looking at the body's reaction to the presence of the virus. The measure of the amount of virus in an individual's blood stream is called the viral load.
Antibodies are produced by the body in reaction to the presence of a virus. In an HIV antibody test, the presence of antibodies in response to the presence of HIV is measured. The most common HIV antibody tests are ELISA (EIA) and Western Blot. These tests can now be performed on samples of oral (mouth) fluid.
If an HIV antibody test is negative, no antibodies were detected. A negative test can indicate that a person is not infected with HIV (s/he is HIV negative), or that s/he has been exposed but the immune system has not had time to produce antibodies. Antibodies to HIV may take up to six months to develop after the initial exposure.
A positive HIV antibody test means that the body has been exposed to HIV (and the body has produced antibodies in response to this exposure). A test result is not reported as positive until it has been confirmed three times, including the use of a different type of test. When a person has a positive HIV test, it does not mean that the person has AIDS or that the person will have AIDS in a certain amount of time--it only means that the person is infected with HIV.
An HIV antibody test may also be indeterminate or inconclusive. In this case, the presence or absence of HIV antibodies cannot be confirmed. An indeterminate test should be repeated three to six months later with a new blood sample.
ELISA - The ELISA (Enzyme Linked Immuno Sorbent Assay), or EIA, is the most commonly used HIV antibody test. It is a highly sensitive test, meaning that all (or nearly all) infected people will test positive.
Western Blot - The Western Blot test is most commonly used to confirm a positive ELISA test. It is more specific than the ELISA test, so all or nearly all people who are not infected will test negative. The two tests combined result in nearly 100% accuracy.
Other Tests - Other diagnostic tests include PCR (Polymerase Chain Reaction), which can detect the virus before the body produces antibodies, and viral culture, where a culture of the virus is produced from a blood sample. Additional tests may be used to assess the functioning of the immune system as a measure of the progression of HIV disease.
A viral load test is a simple blood test that determines both how active HIV is in the body and how well any antiviral therapy medications are working.
Regardless of what type of specimen is used (blood or oral fluid), ELISA is the first test performed. If the first ELISA test is positive, two additional ELISA tests are performed on the same specimen. If both of these tests are also positive, a Western Blot test is performed. A person is said to have a positive antibody test (to test positive) only when each of these tests is positive. HIV antibody test results may take from two to six weeks to be returned.