On Mar. 14, 1996, the U.S. Food and Drug Administration (FDA) announced the approval of the first antigen test kit to screen blood donors for HIV-1, the virus that is responsible for the vast majority of AIDS cases in the U.S.

Previously, blood donors were screened with tests that detect HIV antibodies, which typically appear within three months after infection and indicate the body is responding to the infection. In contrast, antigens, which are the virus’ own proteins, can be detected about one week earlier than antibodies.