HIV tests are used to detect the presence of the human immunodeficiency virus, the virus that causes acquired immunodeficiency syndrome, in serum, saliva, or urine.HIV tests are typically performed on blood or oral fluid. They may also be performed on urine. A NAT looks for the actual virus in the blood and involves drawing blood from a vein. The test can either tell if a person has HIV or tell how much virus is present in the blood (known as an HIV viral load test).