How do antibody-based tests detect how HIV infection works?
After the infection by the HIV the immune system starts the production of antibodies (primary immune response) against the virus. The tests ELISA (enzyme-linked immunosorbent assay) and Western-blot search for the presence of exact antibodies against HIV antigens in blood samples. As only one positive ELISA is not conclusive, as false positive tests may occur, the Western-blot test is often used after the positive ELISA.