On pep for potential sex exposure to hiv. dr says test at week 4 post-exposure (when pep complete). understand pep extends window to 3-6 months post exposure to be conclusive. how much comfort can be taken from this 4-week test? are there any stats?

Tells if has hiv: The test at week 4 post- exposure test p24 antigen of the hiv virus and test antibody if you have developped at the same time. If p24 comes positive you are infected and if negative you may not be infected so negative is not conclusive but positive is a conclusive. If antibody test comes positive you are infected but to rule out false positive possibility you are going to have another test.

HIV test after PEP: No, there are no statistics on this -- i.e. no scientific data on how long positive blood tests might be delayed if PEP doesn't work. Most experts agree that negative results 4 weeks after taking PEP are very reassuring, but as you apparently have heard, it is true that some experts recommend testing as late as 3 months after finishing PEP. Some might say 6 months, but that's probably unnecessary.