My last sexual risky act was 4 months ago exactly. I just started PEP for a different recent/risky sexual act that occurred a week ago. I did an Oraquick test today, one week into PEP and it came back negative.  Am I able to rule out that the first sexual act (that occurred 4 months ago) did not transmit?  Would me taking PEP currently interfere with the test results for an event that occurred 4 months ago? My guess is that the antibodies would be present if infected and thus show up on tests, regardless of being on PEP now for a different event.

Your question is slightly confusing:  My last sexual risky act was 4 months ago" yet you ask about another one only a week ago. I assume both exposure are true.

The oral fluids HIV test (Oraquick) is the last test anyone should use when concerned about a particular exposure. It remains negative in 2-5% of HIV infected people, no matter when they are tested. That said, certainly it would detect 95-98% of infections, and at that level it is reliable evidence you were not infected with HIV 4 months ago. In other words, the answer to your question is no:  taking PEP currently has no effect on an HIV infection that might have been acquired a few months earlier. That is, you are correct hat "antibodies would be present and thus show up on tests regardless of being on PEP...."

For absolutely conclusive testing, have an antigen-antibody (AgAb, "combo", 4th generation) blood test; or an HIV RNA PCR test. However, if I were in your situation I would not be at all worried. It is exceedingly unlikely you have HIV.

I hope this response is helpful. Let me know if anything isn't clear.

HHH, MD