If you think you might have been exposed to HIV, get tested. But testing right away may not pick up early HIV infection. The first HIV test taken soon after infection may say that you do not have HIV even if you do. That is because some HIV tests look for antibodies (the body's natural immune response to a foreign invader) that your body may not have developed yet.
If you get HIV, your body will usually begin to develop antibodies within three to 12 weeks (21 to 84 days). The time between being exposed and developing antibodies is called the "window period."
There are newer HIV tests available that can tell whether you are HIV-positive early after exposure to the virus. One of the newer tests looks for the virus itself, by testing for viral load (the amount of HIV in your blood) and a marker on the virus called p24 antigen. This test is much more sensitive. It can detect HIV within nine to 11 days after exposure. This type of test may be more expensive. Ask your doctor if this test is available when you get tested for HIV.