Anucleic acid test(NAT)can usually tell you if you are infected with HIV 10 to 33 days after an exposure. Anantigen/antibody testperformed by a laboratory on blood from a vein can usually detect HIV infection 18 to 45 days after an exposure. Antigen/ antibody tests done with blood from a finger prick can take longer to detect HIV (18 to 90 days after an exposure). When the goal is to tell for sure that a person does not have HIV, an antigen/antibody test performed by a laboratory on blood from a vein is preferred. Antibody testscan usually take 23 to 90 days to reliably detect HIV infection. Most rapid tests and home tests are antibody tests. In general, antibody tests that use blood from a vein can detect HIV sooner after infection than tests done with blood from a finger prick or with oral fluid.