Mar 21, 2009
There has been a recent recurrence of the "test window" debate. The CDC guidelines can seem murky, but on their page titled, "Should I get tested?," they make it clear:
From the CDC
How long after a possible exposure should I wait to get tested for HIV?
Most HIV tests are antibody tests that measure the antibodies your body makes against HIV. It can take some time for the immune system to produce enough antibodies for the antibody test to detect, and this time period can vary from person to person. This time period is commonly referred to as the “window period.” Most people will develop detectable antibodies within 2 to 8 weeks (the average is 25 days). Even so, there is a chance that some individuals will take longer to develop detectable antibodies. Therefore, if the initial negative HIV test was conducted within the first 3 months after possible exposure, repeat testing should be considered >3 months after the exposure occurred to account for the possibility of a false-negative result
Testing anytime greater than 3 months can rule out the possibility of a false negative result in the first 3 months after exposure.
The CDC no longer states that it is necessary to test greater than 6 months.