[Question #6368] Re-Testing and CDC Guidelines

16 months ago
Dear Drs Handsfield, Hook, and Nurse Warren,

My question relates to the CDC's updated "6 week" guidelines for the fourth generation HIV test, of which I recently became aware. For context, I am a heterosexual female. Two years ago I had a one-off vaginal sex encounter with a heterosexual European male of unknown status. The encounter, while unprotected, did not culminate in ejaculation in me. At 39 days post-encounter, I had a full STI and HIV panel pulled and all results were negative. The HIV test was a fourth generation Ag/Ab with blood taken from the vein. At the time I believed it was conclusive based on the most current recommendations, and so I did not re-test.

Do I need to be re-tested for HIV because my Ag/Ab was pulled at 39 days and not 42, as the CDC now recommends? If so, which test do you recommend?

Thank you very much for your time.
Edward W. Hook M.D.
Edward W. Hook M.D.
16 months ago

Welcome to our Forum. I'll be glad to comment.  The bottom line is that there is no meaningful difference in the reliability of your test results between 39 and 42 days.  There are a number of reasons which contribute to this conclusion.  For your information I have listed several of them below which should be considered in all, rather than one-by-one.

1.  Your encounter was low risk.  Most heterosexual men do not have HIV.

2.  Even in the unlikely event that your partner had HIV, transmission of HIV is a rare event, occurring less than once for every 1000 acts of unprotected intercourse.  the fact that ejaculation did not occur probably makes the exposure even lower risk.

3.  By 28 days nearly all (well over 99%) persons who have acquired HIV will have positive tests.  Our colleagues at CDC tell us that there are "a few" persons who developed positive tests after 28 days but this occurs so rarely that there are no scientific studies which precisely define the frequency.  None of us on this forum have ever seen or heard of such a person.

Bottom line.  You are in the clear for the event you describe and there is no need for further testing related to it.  I hope this information is helpful to you.  EWH