p24 Antigen Test
Formal name: Protein 24 capsid antigen
Related tests: HIV antibody test
The Test
How is it used?
The p24 test may be used to detect early HIV infection and to screen donated blood for HIV. Since p24 levels rise and fall with HIV levels, the test may also be used to monitor anti-HIV therapy and to evaluate disease progression. The advantages of the p24 test are that it can detect HIV infection days earlier, before antibodies develop, and that it is a quantitative test that shows the intensity of HIV expression in the body, which is a measure of how fast the disease is progressing.
When is it requested?
A p24 test may be requested if you have been recently exposed to HIV and wish to know your HIV status, or if you already have HIV and your doctor wants to monitor your response to therapy or to determine if HIV is progressing into AIDS. It is also requested if you are donating blood.
What does the test result mean?
A positive result means that you are infected with HIV: the more p24 protein, the higher the amount of HIV in your blood. A negative test does not exclude HIV infection.
Is there anything else I should know?
The p24 test is one of the earlier tests developed to detect HIV infection. Because p24 is only detectable during a short window of time, its utility is limited. However, this test can still be used when other tests are unavailable.
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