Window periods

With one exception, all the currently available rapid tests look for antibodies only, which means that their window periods are at least as long as those of third-generation tests. (As described above, this is estimated to be between three and six weeks.)

However, when tested against blood samples of people during seroconversion, rapid tests have tended to detect infection a few days later than conventional third-generation tests.

Moreover comparison tests between different rapid tests often show a wide range in performance.^{1 2 3 4} Details from these evaluations, when available, are described in the section on accuracy, below.

However, the potential of a rapid test to detect recent infection has been substantially changed by the introduction in 2009 of the first combination rapid test for antibodies and p24 antigen (Determine HIV-1/2 Ag/Ab Combo). This test’s window period is likely to be close to that of conventional fourth-generation tests.

If the result of a rapid test is non-reactive but there has been a recent high-risk exposure, some testing sites may take a blood sample for laboratory analysis with a fourth-generation test.