This test looks for the presence of Human Immunodeficiency Virus (HIV) 1 and 2 antibodies, and also for antibodies to a part of the virus particle known as p24. This virus protein is detectable in the blood before antibodies are made to the HIV particle, meaning it allows for earlier detection of HIV if present. Once established, the p24 antibodies diminish - so the p24 test a test for diagnosis, whereas HIV antibodies when present suggest an established infection with HIV.