A series of blood screenings are performed to test for HIV. The enzyme-linked immuno assay (ELISA or EIA) is the first test that your doctor will order to screen for HIV. ELISA and the Western blot test detect HIV antibodies in your blood. Antibodies are proteins your immune system produces in response to the presence of foreign substances such as viruses. If you test positive for HIV on the ELISA test, your provider will order the Western blot test to confirm HIV infection.