What is the window period for an HIV test?

What is the window period?

The window period is time between HIV infection and the point when the test will give an accurate result. 

During the window period a person can have HIV and be very infectious but still test HIV negative. 

The window period for a 4th generation antigen/antibody test is about four weeks. By this time 95% of infections will be detected (see Figure 7). There is a three month window period after exposure, for the confirmatory result to detect more than 99.9% of infections.

Figure 7: Time to develop antibodies:

95% people do this by week 4 and more than 99.9% by week 12

Figure 8 shows the range of times that people can take to respond to HIV infection.

The earliest marker is HIV viral load. This is in the first weeks after infection (usually from 1 to 6 weeks after exposure). A high viral load is related to seroconversion symptoms.

The first HIV protein (antigen) that can be measured is p24 (from 1 to 8 weeks after exposure).

Viral load and p24 tests are not accurate for diagnosing early HIV if the results are negative.

An HIV antibody response can be detected as early as two weeks in a few people and in more than 99.9% of people by 12 weeks. An antibody test at 4 weeks will detect 95% of infections.

Antibody testing at 4 weeks can give you a good indication of your HIV status, but you need a test at 12 weeks after the exposure to be considered HIV negative.

Figure 8: Timeline for HIV infection, immune responses and window period for tests

Last updated: 1 December 2019.