P-24 antigen

P-24 antigen A structural protein that is found only in the HIV virus. Tests for the level of P-24 antigen may be done to detect early HIV infection and to screen donated blood for the presence of HIV. P-24 antigen is only detectable during a limited period of time; after the infection has established itself and antibodies have been produced, levels of P-24 antigen usually are not detectable. See also HIV; HS test; P-24 antibody.