I had an encounter with a with a transexual CSW 4 weeks ago where I performed protected oral and received protected oral as well as received protected anal without ejaculation.  I did not personally inspect the condom after the anal and cannot confirm that it didn't break, but was told by my partner that it was intact and don't have any reason to think that was not the case.  

Welcome to the Forum and thanks for the question. Several years ago Dr. Handsfield regularly told clients that at 4 weeks 4th generation combination HIV antigen/antibodies were conclusive at 4 weeks.  Since then the CDC, an institution which is inherently conservative, has revised is assessment to state that results are no entirely conclusive until 6 weeks following an exposure.  As a result and out of respect for our colleagues at CDC we now use that figure and tell clients that at 4 weeks tests results are at least 98-99% conclusive.  That said, neither of us has seen or heard of a person with a 4th generation test which was negative at 4 weeks whose test then became positive.  Your need to re-test at 6 weeks if a personal matter,  As you point out, condom protected sex is safe sex and the evidence from your 28 test is very, very strong evidence that you were not infected.  Were I you, I would not feel the need to re-test but, of course, that is a personal decision.  EWH---

Thank you for the information.  Based on my risk which was low to begin with (condom protect receptive anal and condom protected mutual oral), it sounds like my negative 4th generation duo HIV test at 4 weeks should be all I need to be confident that I am not infected and can safely resume relations with my girlfriend again.

My thinking is that the absolute worst case scenario is that the condom failed in some way that I was not aware of (unlikely) and that my partner was HIV positive.  But even in that worst case situation, I am still looking at about a 1% chance of becoming infected from receptive anal sex and an only about a 1% chance that the "duo" test at 4 weeks did not detect that infection.  According to my math, that would be my worst case scenario risk at about 1 in 10,000 at the most, and most likely more like 1 in a million.

Am I thinking about this correctly?

Yes, you are thinking about this clearly. Your partners HIV status is unknown and most people, even most transsexuals do not have HIV.---