Normal Values:

A negative test result is normal. However, people with early HIV infection (termed acute HIV infection or primary HIV infection) often have a negative test result.

What abnormal results mean:

A positive result on the ELISA screening test does not necessarily mean that the person has HIV infection. Certain conditions may lead to a false positive result, such as Lyme disease, syphilis, and lupus.

A positive ELISA test is always followed by a Western blot test. A positive Western blot confirms an HIV infection. A negative Western blot test means the ELISA test was a false positive test. The Western blot test can also be unclear, in which case more testing is done.

Negative tests do not rule out HIV infection. There is a period of time (called the "window period") between HIV infection and the appearance of anti-HIV antibodies that can be measured.

If a person might have acute or primary HIV infection, and is in the "window period," a negative HIV ELISA and Western blot will not rule out HIV infection. More tests for HIV will need to be done.