Expert: Kristen Brannock, MPH - 3/31/2009

Question
My question is about HIV testing. I have been reading about it on the web and there is a lot of mixed information.

Most of the time, when someone asks about how long to wait before an HIV test is effective.. the answer is 3 month and another at 6 month. But from what I have read, this was the case with the old 1st generation tests and it seems they window has been considerably reduced by the 2nd, 3th and 4th generation tests (some pages say that the 4th generation tests are effective after 2 weeks… other say after 28 days…).
 
Do you have information on this subject, can you clarify what the window for a 4th generation test is, for example for the Abbott AxSYM-HIV Ag/AB test?

Answer
The reason that there is conflicting information is because part of defining the window period rests on each individual. They can say, on average, the window period is x-y for a particular test. While one person may develop antibodies quickly another may take a long time to develop them- which is why some people will say the window period can last as long as 6 months. But only a very small number of people will take that long.

The test that you asked about is a test that looks for anitbodies AND antigen. So, it is a much stronger test than one that looks only for antibodies.