Antibody test results for HIV are accurate more than 99.5% of the time. Once blood has been taken, an Elisa test is used to test for HIV antibodies. A positive test result is then confirmed with a Western blot test.
 
Two special cases have been known to give false results:

1. Children born to HIV-positive mothers may have false positive test results for several months because mothers pass infection-fighting antibodies to their newborn children. Even if the children are not infected, they have HIV antibodies and will test positive. Other tests, such as a viral load test, must be used to confirm results.
2. People recently infected with HIV may test negative if they get tested too soon after being infected with HIV.