HIV testing types
There are three broad types of tests available: antibody tests, combination or fourth-generation tests, and nucleic acid tests (NAT). HIV tests may be performed on blood, oral fluid, or urine.
Most HIV tests, including most rapid tests and home tests, are antibody tests. Antibodies are produced by your immune system when you’re exposed to viruses like HIV or bacteria. HIV antibody tests look for these antibodies to HIV in your blood or oral fluid. In general, antibody tests that use blood can detect HIV slightly sooner after infection than tests done with oral fluid.
It can take 3 to 12 weeks (21-84 days) for an HIV-positive person’s body to make enough antibodies for an antibody test to detect HIV infection. This is called the window period. Approximately 97% of people will develop detectable antibodies during this window period. If you get a negative HIV antibody test result during the window period, you should be re-tested 3 months after your possible exposure to HIV.
With a rapid antibody screening test, results are ready in 30 minutes or less.
A combination, or fourth-generation, test looks for both HIV antibodies and antigens. Antigens are foreign substances that cause your immune system to activate. The antigen is part of the virus itself and is present during acute HIV infection (the phase of infection right after people are infected but before they develop antibodies to HIV). If you’re infected with HIV, an antigen called p24 is produced even before antibodies develop. Combination screening tests are now recommended for testing done in labs and are becoming more common. There is now a rapid combination test available.
It can take 2 to 6 weeks (13 to 42 days) for a person’s body to make enough antigens and antibodies for a combination, or fourth-generation, test to detect HIV. This is called the window period. If you get a negative combination test result during the window period, you should be retested 3 months after your possible exposure.
A nucleic acid test (NAT) looks for HIV in the blood. It looks for the virus and not the antibodies to the virus. The test can give either a positive/negative result or an actual amount of virus present in the blood (known as a viral load test). This test is very expensive and not routinely used for screening individuals unless they recently had a high-risk exposure or a possible exposure with early symptoms of HIV infection.
It can take 7 to 28 days for a NAT to detect HIV. Nucleic acid testing is usually considered accurate during the early stages of infection. However, it is best to get an antibody or combination test at the same time to help the doctor interpret the negative NAT. This is because a small number of people naturally decrease the amount of virus in their blood over time, which can lead to an inaccurate negative NAT result. Taking pre-exposure prophylaxis (PrEP) or post-exposure prophylaxis (PEP) may also reduce the accuracy of NAT if you have HIV.
Talk to your health care provider to see what type of HIV test is right for you.
After you get tested, it’s important for you to find out the result of your test so that you can talk to your health care provider about treatment options if you’re HIV-positive. If you’re HIV-negative, continue to take actions to prevent HIV, like using condoms the right way every time you have sex and taking medicines to prevent HIV if you’re at high risk.
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