Thank you for your question.
Fourth-generation tests look for both antibodies AND antigens. Antigens are proteins on the surface of the HIV particle. Antibodies are produced by the immune system in response to the HIV antigens. They fit together like a lock and key.
The p24 tests are fourth generation tests as are Tri-Dot and Duo tests.
3rd generation tests take 6-8 weeks (usually clinics say 3 months) and is only test for antibodies. 2nd generation tests take a few weeks longer after infection before they are able to recognise infection.
4th generation tests are accurate 3-4 weeks after exposure, because this is when the p24 antigen becomes high enough to measure. Everyone makes antibodies at slightly different rates so to make sure the tests are accurate they air on the side of caution and say you should get the tests done at 28 days.
A negative result at 28 days is good news but it is not conclusive. UK guidelines (BASHH) say that an early negative result at 28 days needs to be confirmed with a second test 90 days after the exposure.
Most private clinics will use the same tests as free clinics. To check the standard of care of the clinic you are interested in using please follow this link
Information on this website is provided by treatment advocates and offered as a guide only. Decisions about your treatment should always be taken in consultation with your doctor.