Hiv rna test negative 12 days after finishing 28-day pep regimen. is it possible the test missed the virus because of the pep, even after 12 days?

Possible: You need to repeat the HIV RNA test at 6 months after exposure to be sure that you are free of the virus. Wish you good health.

Need to wait 3 mo.: Probably your result is valid. However, in theory PEP might prolong the period from exposure to a positive test, if PEP doesn't work. But there are no data. Most HIV experts recommend waiting until 3 months after PEP for a conclusive Ag/Ab (duo) test. This is one reason PEP should only be done for good reason, i.e. truly high risk exposures. It prolongs the anxiety period until conclusive testing.