The window period refers to that point of time after exposure where attest is not able to detect and establish that infection has occurred even if infection has occurred. This is a characteristic dependent on the test. In general there are three main types of tests available. The first type of test which is the most well known and commonly used is the antibody test such as ELISA. These tests are able to pickup infection. The more recent generations of these tests is able to establish whether someone has acquired HIV or not typically within 6 weeks. But most guidelines will tell you that the window period associated with this test arrive at about 99.5 to 99.9% accuracy is the 3 month period. Second type of test is the combination antigen and antibody test. This is called the 4th generation antigen-antibody test. The window period associated with this test is just 3 to 4 weeks. So within 3 weeks this test is able to determine whether someone after exposure acquired HIV infection or did not. So the window period associated with this test to be very conservative is about 4 weeks. The most sensitive test with the shortest window period is the viral load test. The viral load test is the first clinically available test that can become positive. The window period associated is between 7 and 10 days. So as early as 10 days of exposure if infection has to reoccur a viral load test or the HIV-RNA-PCR test becomes positive. So the window period associated with that is about 10 days.

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