What kinds of tests are available, and how do they work?
There are three types of tests available: nucleic acid tests (NAT), antigen/antibody tests, and antibody tests. HIV tests are typically performed on blood or oral fluid. They may also be performed on urine.
- A NAT looks for the actual virus in the blood and involves drawing blood from a vein. The test can either tell if a person has HIV or tell how much virus is present in the blood (known as an HIV viral load test). While a NAT can detect HIV sooner than other types of tests, this test is very expensive and not routinely used for screening individuals unless they recently had a high-risk exposure or a possible exposure and have early symptoms of HIV infection.
- An antigen/antibody test looks for both HIV antibodies and antigens. Antibodies are produced by your immune system when you're exposed to viruses like HIV. Antigens are foreign substances that can cause your immune system to activate. If you have HIV, an antigen called p24 is produced even before antibodies develop. This lab test involves drawing blood from a vein. There is also a rapid antigen/antibody test available that is done with a finger prick.
- HIV antibody tests only look for antibodies to HIV in your blood or oral fluid. 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. Most rapid tests and the only currently approved HIV self-test are antibody tests.
Talk to your health care provider about what type of HIV test is right for you.
How long does it take to get results?
- Laboratory tests (NAT and antigen/antibody) require blood to be drawn from your vein into a tube and then that blood is sent to a laboratory for testing. The results may take several days to be available.
- With a rapid antibody screening test, usually done with blood from a finger prick or with oral fluid, results are ready in 30 minutes or less.
- The rapid antigen/antibody test is done with a finger prick and takes 30 minutes or less.
- The oral fluid antibody self-test provides results within 20 minutes.
How soon after exposure to HIV can a test detect if I have the virus?
No HIV test can detect HIV immediately after infection. If you think you've been exposed to HIV in the last 72 hours, talk to your health care provider about post-exposure prophylaxis (PEP), right away.
The time between when a person may have been exposed to HIV and when a test can tell for sure whether they have the virus is called the window period. This window period varies from person to person and depends on the type of test used to detect HIV. Ask your health care provider or test counselor about the window period for the test you're taking.
- A nucleic acid test (NAT) can usually tell you if you have HIV infection 10 to 33 days after an exposure.
- An antigen/antibody test performed 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).
- Antibody tests can take 23 to 90 days to detect HIV infection after an exposure. Most rapid tests and self-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.
If you get an HIV test after a potential HIV exposure and the result is negative, get tested again after the window period. Remember, you can only be sure you are HIV-negative if:
- Your most recent test is after the window period.
- You haven't had a potential HIV exposure during the window period. If you do have a potential exposure, then you will need to be retested.