Types of HIV Tests
Reviewed by: HU Medical Review Board | Last reviewed: September 2019 | Last updated: March 2020
Since HIV symptoms are often non-specific, or not present at all, they are not reliable in determining if you have the virus. The only way to be certain of your HIV status is to get tested. The timing of when to get tested depends on how long ago a potential exposure occurred and what kind of test is used.
If you think you have recently been exposed to HIV, seek medical attention as soon as possible. Post-exposure prophylaxis (PEP), a medication used to prevent the spread of the virus after exposure has already occurred, may be beneficial. PEP can only be used within 72 hours (three days) of exposure, so the sooner a healthcare provider is contacted after potential exposure, the better.1
HIV testing window period
Immediately after a person is infected with HIV, they will not test positive for the virus. This period of time, when an individual has HIV but it cannot be detected on testing, is called the window period. Some tests for HIV look for specific antibodies in the blood. Antibodies against HIV are proteins in the blood made by your immune system that are created specifically to fight the virus. An individual who does not have HIV will not have these antibodies. It takes a few weeks, or even months, for these antibodies to develop and to be present in high enough amounts to be detected on HIV tests. Other tests can look for the virus itself in your blood, or proteins made by the virus. However, it still takes some time for enough of the virus and its proteins to build up in the blood and be detected by tests.1-4
Each test has a different window period, with the shortest window period being about ten to 33 days after infection.1 However, as mentioned, if you think you have been exposed very recently, you may be eligible for PEP if the exposure was within the past few days. Your doctor, healthcare provider, or testing facility will know the window period for the specific test used on you. If you’re using an at-home test, the instructions should include information on the window period for the test you have. If you test negative for HIV, but are within the window period for your test, you may not be HIV-negative. Follow-up testing later on may be required.
Tests for HIV
There are a variety of different tests available for HIV. Some of the most common tests include the following:
- Nucleic acid tests (NATs): NATs have the shortest window period for detecting HIV infection, and can typically detect the virus about 10 days to a month after exposure. NATs work by looking for HIV RNA in the blood. This is the virus’ genetic material, and shows that HIV is in your blood and replicating. NATs are generally only used when a person has had a recent exposure to HIV and is showing early-stage, flu-like symptoms. NATs are expensive and not typically used in routine screening.
- Antibody tests: As mentioned, when the body is infected with HIV, it begins to make antibodies against the virus. Antibody tests look for HIV-specific antibodies in the blood. Only an individual who is infected with HIV will have these. Someone who does not have HIV will not. Antibody tests may require an oral fluid or a blood sample from the finger or from a vein in the arm. Tests that come from venous blood can usually detect the virus sooner than tests that use oral fluid or finger-prick blood. The time it takes for an antibody test to detect the virus is about 23 days to three months after infection. Some antibody tests are rapid tests, meaning the results can come back in a matter of minutes.
- Antigen/antibody tests: In addition to antibodies, some tests may also look for virus-specific proteins in the blood. These virus-specific proteins are called antigens. Our immune system responds to, and fights off, foreign antigens when they enter our body. One HIV-specific antigen is called p24, which is a protein that is a part of HIV itself. Some tests may be able to detect this antigen sooner than HIV antibodies, and when tested together, may provide an earlier result. These tests require a blood sample. Depending on where a blood sample is taken from, these tests can detect an infection anywhere from 18 to 90 days after infection. Blood taken from the veins can detect the virus sooner than tests that use blood from a finger prick.
- At-home testing kits: At-home kits look for HIV-specific antibodies in the blood. The only FDA-approved at-home testing kit currently available on the market is the OraQuick In-Home HIV test. The OraQuick requires a sample of oral fluid taken using a swab. The results come back in about 20 minutes. If an individual test positive for HIV using the at-home kit, follow-up testing will be required. The manufacturers of the test can connect an individual with further resources, or you can visit your regular doctor or healthcare provider. If you test negative for HIV using the at-home kit, it does not guarantee that you do not have HIV. Some individuals may experience a false negative (get a negative result when they actually do have the virus). If you get a negative result but think you have been exposed to the virus or are at a high risk of getting HIV, follow-up care may be necessary.1-6
After you test positive in a healthcare setting, your blood may need to be tested further to determine your viral load, or how much active virus is present in your body. This information helps your healthcare team guide and monitor your treatment.