This is very useful information. I had an illness starting at 2 weeks after low risk exposure and have taken your tests at 28,29 and 31 days post exposure. I assume that based on 90 percent chance of positive result at 5 weeks that the odds are in my favour based on my 4.5 week test? I was also told online that antibody tests are usually always positive by two weeks after illness if related to hiv. Not sure how true this is. Kind regards Tony - note from PEBL:- this discussion has been posted as a new thread:- http://peblfeedback.com/hivselftest/pebl/testing-window-period/  

Hi Kat This is a difficult thing to predict. We need to use the 12 week window period because the BioSURE HIV Self Test detects antibodies to HIV and different people produce antibodies at different times after infection. There have been a number of studies into this issue and the consensus is that at 5 weeks post infection around 90% of people would have generated the antibodies required. At 6 weeks around 95%. At 12 weeks this increases to 99.9%. So your negative test is very encouraging, but unfortunately is not conclusive. We would strongly recommend that you test again in another 6 weeks. I am sorry that I cannot give a more definitive answer. Kind regards Gary Carpenter BioSure (UK) Limited