The HIV antibody test is the gold standard for HIV diagnosis and is performed in two steps: a primary screening test and a confirmatory test. Primary screening is usually done by ELISA, chemiluminescence, or immunofluorescence testing for HIV antibodies, which can reach a sensitivity of 99% or higher. If the initial screening is negative, the patient is excluded from having HIV. If the initial screen is positive, a confirmatory test should be performed as a next step. If the confirmatory test is negative, the initial screen is false positive and the patient is not infected with HIV. If the confirmatory test is also positive, the patient is infected with AIDS and should be treated with antiretroviral drugs as soon as possible to avoid progression to the AIDS stage.