Antibodies against HIV-1 and HIV-2 are usually not detectable until 6 to 12 weeks following exposure and are almost always detectable by 12 months. They may fall to undetectable levels (ie, seroreversion) in the terminal stage of AIDS when the patients immune system is severely depressed. However the addition of antigen named p24 assist in detecting the status of HIV even before your body has a chance to make antibodies to the virus. The p24 antigen test is accurate 11 days to 1 month after getting infected with HIV1/2. The p24 antigen becomes undetectable once body start making antibodies against the virus.