There are three main types of HIV tests: antibody tests, combination tests (antibody/antigen tests), and nucleic acid tests (NATs). How soon each test can detect HIV infection differs, because each test has a different window period. The window period is the time between when a person gets HIV and when a test can accurately detect HIV infection.
- Antibody tests check for HIV antibodies in blood or fluids from the mouth. HIV antibodies are disease-fighting proteins that the body produces in response to HIV infection. It can take 3 to 12 weeks for a person’s body to make enough antibodies for an antibody test to detect HIV infection. (In other words, the window period for antibody tests in most people is somewhere between 3 to 12 weeks from the time of infection.) In general, blood testing is more accurate than oral fluid testing.
- Combination tests (antibody/antigen tests) can detect both HIV antibodies and HIV antigens (a part of the virus) in blood. It can take 2 to 6 weeks for a person’s body to make enough antigens and antibodies for a combination test to detect HIV infection.
- Nucleic Acid Tests (NATs) look for HIV in the blood. NATs can detect HIV infection about 7 to 28 days after a person has been infected with HIV. NATs are very expensive and not routinely used for HIV screening unless the person had a high-risk exposure or a possible exposure with early symptoms of HIV infection.A person’s initial HIV test will usually be either an antibody test or a combination test. If the initial test result is positive for HIV infection, then follow-up testing will be done to make sure that the diagnosis is correct. If the initial test result is negative and the test was done during the window period, re-testing should be done 3 months after the possible exposure to HIV.HIV tests can be conducted in laboratories, at home, in non-clinical settings and in clinical settings. Simple, rapid test methods are available that produce results in as little as 60 seconds. The CDC has posted links to information on testing resources for FDA-approved laboratory tests and home tests. Learn more about testing in nonclinical settings and testing in clinical settings. Your doctor can help you figure out which type of test is best for you.