Elisa Test – The initial blood test for HIV infection. The test detects HIV antibodies based on a reaction, which leads to color change in a test tube. The Elisa is often used as the initial screening test because it is easy to-do and it is not expensive. Since this test detects all persons with HIV antibodies as well as some persons who don’t have HIV antibodies (called false positives), a positive Elisa test must be confirmed by another more specific test called the Western Blot Test. More information on HIV/AIDS is provided in our HIV/AIDS Section.