ANNOUNCER: There are two major classes of HIV tests.
JEFFREY LAURENCE, MD: What most people commonly refer to as an HIV test or, colloquially, as an AIDS test is a test for antibodies to the virus. And, in this disease, unlike virtually any other disease, if you have antibodies to the virus, you have that virus active in your blood.
The second type of test is testing for the virus itself. Those tests are a bit more complicated. They're usually only done if we already know that you have antibodies against the virus and we want to measure how much virus do you have floating around in your blood.
ANNOUNCER: The standard HIV tests were first developed in 1985, and while highly accurate, they are also time consuming.
JEFFREY LAURENCE, MD: If someone requests a test for HIV or a physician orders one, there's first, some pretest counseling that is done.
Then, typically, a blood sample is drawn. And you go through a waiting period. That waiting period, depending on the clinic may be anywhere from a week to two weeks. And during that period of time, a screening test is done known as an ELISA test, which tests for antibodies against the virus itself. And, if that test is negative, then no further testing is done.
If that test turns out to be positive, it's incredibly important for the laboratory to determine if that's a true positive or just some false positive, and that second test is called a Western blot.