I’ve been having problems with my insurance and wasn’t able to start taking my prep meds until about a week afterwards. I realize taking prep after the fact wouldn’t help with a previous exposure. I took an RNA test 25 days after exposure and a 4th gen lab antigen(and pcr/rna) test at about 34 days after and the results were negative. Question is: did taking the prep elongate my test window and I shouldn’t  be confident in the results? 

Honestly, I don't see anything especially "unique" about this event; at least the potato chip business makes no difference in your risk of HIV, even if your partner was infected -- which he probably was not. Even if your partner had active, untreated HIV, your chance of catching the virus would have been roughly one in 10,000 according to a risk estimate published by CDC. That's equivalent to giving BJs to infected men once daily for 27 years before it would be likely you would catch the virus. But even more important, your negative RNA test. at 25 days is 100% proof you were not infected; in newly infected people, the RNA test is positive 100% of the time by day 11.

Given the low risk of the event -- regardless of the potato chip, or even if you had obvious open sores in the mouth -- you should not have sought or taken PEP. And you are right that staring a week after exposure was dumb:  even if you had legitimately been exposed to HIV, it could not have lowered the chance you were infected. Did it delay a possibly positive test? No, not by this long. The tests you had would have been positive within a week or two of your last dose of anti-HIV drugs.

All is well; you're not infected. Don't worry about it.

HHH, MD

You said, below, that I would have tested positive a week after stopping pep…. Since I’m still taking Descovy, should I not trust the negative pcr tests? 

Routine PrEP procedures include regular HIV testing from time to time, with the frequency depending on the type and frequency of ongoing exposures. If fellatio (giving and receiving) will be your only exposures, I would say testing once a year would be fine. PrEP is considered so effective that the only way to become infected is to be exposed to an HIV strain resistant to Descovy (or whatever product is used for PrEP. Therefore negative testing while on treatment is considered reliable.

I really appreciate you being patient with me… I’m sure you deal with anxious people constantly 

Apologies for the long delay in answering this follow-up question.

That concludes this thread. I hope the discussion has been helpful.