Follow-up diagnostic testing is performed if the first immunoassay result is positive. Follow-up tests include; an antibody differentiation test, which distinguishes HIV-1 from HIV-2; an HIV-1 nucleic acid test, which looks for virus directly, or the Western blot or indirect immunofluorescence assay, which detect antibodies.
Immunoassays are generally very accurate, but follow-up testing allows you and your health care provider to be sure the diagnosis is right. If your first test is a rapid test, and it is positive, you will be directed to a medical setting to get follow-up testing. If your first test is a lab test, and it is positive, the lab will conduct follow-up testing, usually on the same blood specimen as the first test.
False-positive tests are rare. If tests are conducted during the window period, they can give a false-negative result.
Currently there are only two home HIV tests: OraQuick In-home HIV test and the Home Access HIV-1 Test System. If you buy your home test online make sure the HIV test is FDA-approved.