One of my most common questions is around the accuracy of the rapid HIV test in the 90 days of the window period.
To help answer this question I have created a graph to show how the test becomes more sensitive, that is more able to detect HIV infection, during the window period.
With all HIV tests we are not looking for HIV virus directly. We look for antibodies against HIV made by the body or for a protein P24 created early after infection with HIV.
The 3rd generation HIV tests look only for the antibodies while the 4th generation HIV tests look for antibodies as well as P24 protein.
After infection with HIV P24 starts to be produced in the first week and can be detected around 15 days post infection. Antibodies take a little longer and can be detected about 18 days after infection.
A quick summary of the graph above:
- Neither HIV test can detect HIV infection earlier that 12 days.
- At 14 days the 3rd generation test will detect 5% of HIV infections, 4th generation tests will detect 21% of HIV infections.
- At 21 days 3rd generation and 4th generation tests are similar detecting over half of HIV infections.
- At 30 days both tests detect over 90% of HIV infections
- At 45 days both tests detect 95% of HIV infections
- At 60 days 3rd generation tests detect 96% of HIV infections, 4th generation tests detect 99% of infections.
- Both tests detect 100% of HIV infections at 90 days.
The rapid HIV test I use at Collins Street Medical is a 4th Generation rapid HIV test made by Alere.
Dr George Forgan-Smith