HIV - Prevention Expert Forum
A Question on Testing
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This forum is limited to prevention of HIV and to safe sex in general. All questions will be answered by H. Hunter Handsfield, M.D. or Edward W Hook, MD.

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A Question on Testing

Hi Drs.
I hope you are well.
My situation is as follows:
I had unprotected oral sex with a csw and possibly unprotected vaginal,i say possibly due to lack of memory from alcohol,in an asian country with a very large commercial sex industry.
I took a Hiv p24 duo test in London after 28 days,which came back negative, and was told by the clinic that this was conclusive.Great,but...after reading many posts on your website,particularly by one of your specialists,Teak,i am being led to believe that my test is reassuring but would not be conclusive until retested at 3 months.
On another well known website specialising in this area,The Body, the doctor on the forum is of the same opinion.
I now find i cannot let myself have unprotected sex with my long term partner and am thinking of retesting duo at 7 weeks.But then,i guess i will still be concerned until a 90 day test comes back negative.
1.I was under the impression that the duo picks up 99.89% of infections after 28 days and a standard latest generation antibody test will pick up 99.99% after 90 days.Is this correct?Not a lot of difference.
2.Would a duo at 7 or 8 weeks increase the 99.89% value and when would it equal the hallowed 90 day test?
3.Finally,why so many discrepancies among specialists?
sorry for such a long post but it will be my only one.
Thanks
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Welcome to the forum.

You had a low risk exposure, since most CSWs even in Asian countries with vibrant sex industries (e.g., Thailand) do not have HIV; oral sex carries little or no risk; and even unprotected vaginal sex carries an average transmission risk of only 1 in 2,000.  But the level of risk is irrelevant anyway; your test results show you weren't infected.

From all you say, your preliminary research came up with entirely accurate information; I agree with the information you learned from the MedHelp HIV community forum (Teak) and Bob Frascino at thebody.com.  To your specific questions:

1,3) Those figures are about right, and there is no discrepancy.  Don't get hung up on the difference between 99.89% versus 99.99%.  (On this forum we just say both results are around 99.9% accurate by 4 and 12 weeks.)  The available data aren't that precise aren't nearly precise enough to judge a difference of only 0.1%.  You should view both the negative duo test at 4 weeks and a negative antibody-nly test at 3 months as proof against a new HIV infection.

2) Testing at 7-8 weeks will make no difference.  You don't need any further testing.

Bottom line:  You didn't catch HIV and don't need any further testing, at least not from a medical/risk perspective.  But feel free to have another test for psychological support, if the repeated reassurance -- from Teak, Dr. Bob, and now me -- doesn't settle it for you.

Regards--  HHH, MD
3 Comments
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Thanks for your reply Dr Hadsfield
I am confident i have not caught Hiv after reading your post.
I do however think you may have misunderstood me.
I stated that Teak and Dr Bob are not of the same opinon as you,and they clearly emphasise that a Duo is not conclusive at 4 weeks and only a 12 week antibody test is.You on the other hand are of the opinion that an 8 week antibody test is conclusive.
This is my last post,please feel free to close this thread,prefferably after a final comment on your part.
Thanks and best wishes.
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239123_tn?1267651214
Thanks for the clarification.  I won't get into a debate with other online resources.  However, I will point out that the moderators of MedHelp's international HIV forum agree that a negative combo (duo) test at 4 weeks is just as definitive as a 3 month antibody test.  Significantly, those moderators are in the UK, where the combo test has been in use for a few years.

The manufacturers' formal advice (and their FDA-approved interpretation) for antibody-only testing is that it can take 3 months to convert to positive, and many American providers and experts tend to stick with that advice for medicolegal safety -- even though there are solid data for 6-8 weeks.  No matter how strong new data may be, the manufacturer of a test may not legally claim a new standard until and unless they conduct their OWN research and submit the results to FDA -- an expensive process, so it rarely happens.  (Same thing when drugs are found to work for medical conditions or in doses which were not initially approved by FDA.  Some of CDC's own recommendations for STD treatment advise drug doses that are not approved by the FDA.)  As long as the manufacturer of a test or drug legally must stick with a certain standard, you can understand why many doctors, health departments, CDC, and other advisors feel compelled to adhere to the same advice.

The combo HIV p24/antibody test has only recently been approved by the FDA for use in the US and there is not yet much clinical experience with it.  My understanding is that the manufacturer has FDA approval to claim 99% (maybe it's 99.9%, I'm not sure) reliability 4 weeks after exposure, and I anticipate this interpretation will gradually diffuse to all US based providers and health departments.  But it may take a while.
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Avatar_n_tn
I too noticed the discrepancy between the Doctor's Forum and the regular Forum with regard to the antibody only test.  I am glad that the doctors' opinion is high probable conclusiveness at 8 weeks.  Thanks for the detailed explanation.
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