P24 Antigen

P24 is a capsid structural protein that makes a protein shell on the surface of the HIV (human immunodeficiency virus). It helps in identifying the actual HIV particles present in the blood. They show a positive result when the test is taken after two to three weeks of HIV infection. P24 protein cannot be detected after a week of HIV infection as the virus takes some time to get multiplied. It is again undetectable when sufficient antibodies to HIV are produced. At this point, the standard HIV antibody test shows a positive result. Later in the course of HIV, it becomes detectable.