The diagnosis of HIV infection can be made by detecting the presence of disease-fighting proteins called antibodies in the blood. These HIV antibodies are not generally seen until 1-3 months following infection. If you have been exposed to the HIV virus, early testing is important because it is generally believed that the earlier treatment is started the better your outcome. Furthermore, high-risk behaviors that could spread the virus to others can be avoided.
Two different types of antibody tests, enzyme-linked immunoassay (ELISA) and Western blot, are available. The screening test is the ELISA test, and Western blot is the confirmatory test. Both of these tests can be negative for up to 3 months after the exposure. In this situation, if the suspicion for HIV infection remains high, another, more accurate test can be performed. This test directly looks for the actual HIV particles in the blood.