For many years, the standard test for HIV infection has been the antibody test. The P24 antigen test is new and different because it is not an antibody test. It was approved by the U.S. Food and Drug Administration (FDA) in 2010 to detect HIV in adults and has been used in the United States since then. The P24 antigen test detects a specific protein produced by HIV during the earliest stages of infection, making it useful for diagnosing acute HIV infection before antibodies develop (about eight weeks after exposure).
The P24 test is a simple blood test that's commonly used to detect HIV early on in the infection. It also has some advantages over other tests because it can be done with just one drop of blood and doesn't require any special training to administer. However, this test is not perfect, and you may need to take more than one sample if your initial results are inconclusive (e.g., borderline positive or indeterminate). Here's how you can accurately interpret your results:
The P24 antigen test, an FDA-approved diagnostic tool for determining early signs of HIV infection, has been promoted for broader use. This test can be used to detect HIV infection as early as two weeks after exposure to the virus, and is estimated to detect more than 90 percent of infections at 20 days after exposure.
Most people with newly acquired HIV don't develop enough antibodies for standard tests to detect until around one month after infection, making the standard antibody test inaccurate for about 80% of all new infections. The P24 antigen test offers a solution: because it can measure the presence of a specific protein that is produced by HIV during the earliest stages of infection (before antibodies have formed), it can accurately identify infected individuals even before they've started producing antibodies themselves.
The test itself simply measures levels of a specific protein produced by HIV during the earliest stages of infection. This protein is present in large quantities during acute HIV infection before antibodies are detectable by standard serological tests, and it is also used to monitor treatment effectiveness.
Most people with newly acquired HIV don’t develop enough antibodies for standard tests to detect until around one month after infection, making the standard antibody test inaccurate for about 80% of all new infections.
The P24 antigen test can fill this gap by detecting this protein which is present in large quantities during acute HIV infection before antibodies are detectable by standard serological tests (ie approximately one to three weeks after exposure).
The P24 antigen test can fill this gap by detecting this protein which is present in large quantities during acute HIV infection before antibodies are detectable by standard serological tests (ie approximately one to three weeks after exposure).
The P24 antigen test is not a substitute for standard antibody tests and must be used in conjunction with them. It should only be done if you have no symptoms of HIV, have had very few sexual partners, or think that you may have been exposed to HIV. The test is expensive, insensitive and it has low specificity meaning that there may be false positives. However, the sensitivity of the test makes it useful for detecting more than 90% of infections at 20 days after exposure which means that many infections will be detected before antibody levels become detectable by other methods such as ELISA/Western blotting
The P24 antigen test is a test that detects the presence of HIV in the body. This test is used to detect HIV infection as early as two weeks after exposure to the virus, but it may take up to 12 weeks after exposure before all antibodies produced by your immune system are detectable. The estimated sensitivity of the P24 antigen test at 20 days after exposure is more than 90 percent; however, some studies have found lower rates of detection when samples were collected less than six days after initial exposure (about 87 percent).
The P24 antigen test is used to detect HIV proteins early on in the infection. The P24 antigen test is not commonly used because of its limited sensitivity and specificity compared to other tests.
The P24 antigen test is easier and less expensive than the HIV antibody test, making it a good first-line screening tool for rare or low prevalence areas where a positive result may lead to further testing with more sensitive and specific tests such as Western blot or immunofluorescence assay (IFA).
The P24 antigen test is not commonly used, and it's designed to detect HIV proteins early on in the infection. The test is not recommended for use in pregnant women.
If you want to use this test in your clinic, we recommend that you work with a specialist who knows how to interpret the results.