The CDC recommends these blood tests. They can detect HIV as soon as 20 days earlier than antibody screening tests. They check for HIV antigen, a protein called p24 that's part of the virus that shows up 2-4 weeks after infection, as well as HIV antibodies. A rapid antibody/antigen test can give you results in 20 minutes. RNA Test. This looks for the virus itself and can diagnose HIV about 10 days after you've been exposed. It's expensive, though, so it's usually not the first test.