Hi Guy Thanks for getting in touch. This will be quite a long explanation, so please bear with me! There are currently 4 generations of HIV test that have been created. The generation describes the mechanism used to capture evidence from your blood with regard to the presence of HIV. The later the generation the earlier that a test should be able to detect HIV. The first 3 generations of tests work by finding antibodies that you have created to the virus. The difference in structure between 2nd and 3rd generation tests means that a 3rd generation test is more sensitive to the earliest forms of antibody created. This difference equates to an average 1 week earlier than a second generation test. The biggest variance in time to detection of HIV for both these kinds of tests actually has very much more to do with the likelihood of the person creating the antibodies at any particular interval after infection. Most people will have made some antibodies by around 3 weeks after infection. A second generation test would be around a week later, so after about 4 weeks. However, some people will not create any antibodies until 12 weeks after infection. So regardless of whether 2nd or 3rd generation neither test can work until the antibodies have been created. 4th generation tests detect antibodies and part of the virus directly. However, these tests are only reliable when performed as laboratory tests and not as a rapid test, like the BioSURE HIV Self Test. The BioSURE HIV Self Test falls into the category of 2nd generation tests. So, a negative test is always very encouraging. A positive result is always equally likely to be correct, regardless of time post possible infection that the result is found. But a negative test can't really be absolutely conclusive until more than 3 months after possible infection. I hope that this helps. Kind regards Gary Carpenter BioSure (UK) Limited