Types of HIV Tests?

What are the types of HIV tests?

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.

What we know about the types of HIV tests:

A lab technician drawing a blood sample from a test tube

HIV tests are very accurate at detecting HIV, but no HIV test can detect HIV immediately after infection. How soon a test can detect infection depends upon different factors, including the type of test being used. In general, nucleic acid tests (NAT) can detect HIV the soonest, followed by combination or fourth generation tests, and then antibody tests.

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 and bacteria. 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.

With a rapid antibody screening test, results are ready in 30 minutes or less.

Home tests are antibody tests you can buy at a pharmacy or online. There are only two FDA-approved home test kits, the Home Access HIV-1 Test System and the OraQuick In-Home HIV Test.

The Home Access HIV-1 Test System is a home collection kit, which involves pricking your finger to collect a blood sample, sending the sample to a licensed laboratory, and then calling in for results as early as the next business day. This test is anonymous. If the test is positive, a follow-up test is needed to confirm your results. The manufacturer provides confidential counseling and referral to treatment.
The OraQuick In-Home HIV Test provides fast results in the home. You have to swab your mouth for an oral fluid sample and use a kit to test it. Results are available in 20 minutes. If you test positive, you will need a follow-up test to confirm your results. The manufacturer provides confidential counseling and referral to follow-up testing sites. Because the level of antibody in oral fluid is lower than it is in blood, blood tests find infection sooner after exposure than oral fluid tests.

If you use any type of antibody test and have a positive result, you will need to take a follow-up test to confirm your results. If your first test is a rapid home test and it's positive, you will be sent to a health care provider to get follow-up testing. If your first test is done in a testing lab and it's positive, the lab will conduct the follow-up testing, usually on the same blood sample as the first test. +

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 time range is called the 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.

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. 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 in the United States. 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 time range is called the window period. If you get a negative combination test result during the window period, you should be re-tested 3 months after your possible exposure.

Nucleic acid tests (NAT) look for HIV in the blood. + 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.

What you can do

Talk to your health care provider to see what type of HIV test is right for you. They can tell you the window period for the type of test you take. If you're using a home test, you can get that information from the materials included in the test's package.

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 or learn ways to prevent getting HIV if you're HIV-negative.

Additional Resources

Learn about the Centers for Disease Control and Prevention's HIV testing campaigns:

Act Against AIDS: Encouraging all Americans to learn more about HIV/AIDS.

Get Tested. National HIV and STD Testing

HIV Screening Standard Care: Encouraging primary health care providers to screen all patients for HIV.