[Question #1637] Potential high risk situation and tests

46 months ago
Hello Doctors,
First of all I would like to congratulate you for the excellent job and information you provide. After reading some of the posts here I got the guts to ask some questions that are making me at least unconfortable.
Eight months ago I had a high risk situation. It was about a sexual encounter I had with a girl and during the foreplay she managed to insert maybe one third of my penis inside her anus, unprotected. I pulled it out and we stopped at that momment. I read about the statistics here but of course I didn't calm down.
Going straight to the point, I talked to my doctor and he told me to do tests for HIV, Hepatitis and Syphillis in 4 weeks and then repeat the HEP B/C and the Syphillis test at 12 weeks. I did all the tests like he told but I also asked for a second HIV test at 12 weeks.

All tests came negative. All the tests were done in a large professional clinical laboratory, and I was told the HIV tests were 4th generarion.

I know my question may sound ridiculous, and it's related with the HIV test, the scary part. Have you ever heard about HIV tests giving false negative with formerly healthy people ? Risking to sound even more ridiculous, are there any chances of a double false ?

I'm asking this because the doctor asked for two test sets and I'm intrigued. Wasn't one enough ?

Thanks for your attention !
Edward W. Hook M.D.
Edward W. Hook M.D.
46 months ago

Welcome to our forum and thanks for your vote of confidence.  Your doctor is being cautious on your behalf.  HIV tests are amongst the most reliable tests available in all of medicine but there is some confusion as to what time they are definitive.  Currently used 4th generation tests provide definitive results at 4 weeks following an exposure even though the manufacturer's instructions state that results are not definitive until 12 weeks after exposure.  I will paste an explanation of the reasons for this that Dr. Handsfield recently wrote because if nicely explains why this occurs. 

" CDC developed its advice before 4th generation tests became available. The first reason is that many government agencies generally take conservative positions on prevention advice, and 3 months does that. Second and perhaps most important:  As a government agency, CDC's advice usually must be consistent with the official information provided by the test manufacturers in the tests' package inserts. That information is based on original research, before the tests were marketed, and much of that research is conducted in a way that probably underestimates the tests' true performance. In any case, that information cannot legally be changed unless and until the test manufacturer conducts and new research to justify the change, and that research is vetted and approved by the US Food and Drug Administration. That's a very expensive process and therefore is rarely done. Other research, or the clinical experience of experts using the tests in the real world, and theoretical considerations about how the tests work may not be used to justify a revised package insert or any other information provided to the public. However, independent experts do not have those restrictions and can give advice based entirely on their clinical experience and their interpretation of the science of the tests and published science. That's what we do on this forum."

thus your first negative test proved that you did not get HIV from the exposure that you described but your doctor was being conservative and following what we consider overly conservative recommendations.  I hope this explanation is helpful to you,.  If anything here is not clear, please let me know.  EWH


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46 months ago
Dr. Hook,

Thank you for you extremely fast reply to my question. I'm glad it was only because an overly conservative position.

Revising my tests, I see now that the first batch didn't include Syphillis, just the second batch.

You said  the 4th gen test are amongst the most reliable tests available and I don't doubt, but are there any chances of false negatives ?
For me, logics tells me that it's nearly impossible to have two failed (false negative) HIV tests.


Edward W. Hook M.D.
Edward W. Hook M.D.
46 months ago
Correct, the likelihood of having two HIV tests miss an HIV infection is effectively zero.  On a single test, estimates are that current tests would miss less (probably substantially less) than 1 in 1000 positive tests.  Since only a very small proportion of all HIV tests are positive, persons can have very great confidence that a single negative HIV test reflects their true infection status.  EWH---
46 months ago
Thank you again for your clear explanation.  The chances of two failed tests are virtually zero (at least less than 1:1 million)

I was not tested for other STDs rather than Hep/Hiv and Syphillis. Do you recommend to be tested for something else even if more than 3 months after the exposition ?
Edward W. Hook M.D.
Edward W. Hook M.D.
46 months ago

Realistically, I see no reason for further testing.  The testing already performed, combined with the brevity of your exposure and the absence of symptoms since then are sufficient to assure me that you did not get an STI from the exposure you have described. My advice is for you to now move forward without concern. 

As i suspect you know,  o ur Forum Guidelines allow up to three replies to a client’s questions.  This will be my third and therefore final reply.  I hope my comments and the information I have provided has been helpful.  Take care.

  EWH

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