p24+ELISA Duo Test accuracy??Please help!

[empgraph]

Hello, I'm sorry my English is not very good, I'm from Europe. I had a risk encounter with a worker 2 months ago, and the condom broke briefly (maybe 5 seconds). 21 days after this, I took a Duo Test of 4th generation (p24 + ELISA), which came back negative. I will wait for the 3 month mark, but until that day arrives, I need to know how reliable is the 4th generation p24 + HIV test. The doctor said it was 98%, but after reading a lot of posts, I think that it is lower than 98% at 3 weeks, the question is: maybe 80-90% aproximately accurate??? There is a big difference for my peace of mind between 60% accurate or 90%, the only reference I have until the 3 months test is this 21 days test, I hope it is reliable. Thank you very much for your help.

[H. Hunter Handsfield, M.D.]

My understanding is that 3 weeks after exposure, at least 90-95% of people with new HIV infections would have a positive result on at least one of the 2 components of the Duo test (P24 antigen or antibody by ELISA).  But that doesn't mean there is a 5-10% chance you have HIV.  If you are a male and had vaginal sex with a broken condom, the odds are very strong that you did not catch HIV.

You don't need to wait 3 months.   A negative antibody test at 6 weeks will be 100% proof you didn't catch HIV.  For more information, read any of a few hundred threads on this forum about time to positive HIV test results.

Good luck--  HHH, MD

[H. Hunter Handsfield, M.D.]

CDC's figures are conservative.  During an HIV/AIDS scientific meeting about a year ago, with about 300 HIV experts in the room, the moderator asked whether anybody had seen a patient with a positive test delayed more than 6 weeks using the newer tests that have been routine in the past few years.  No hands went up.  Even CDC's own advice is that it is never necessary to test beyond 3 months.

My assessment of your risks is not based primarily on the test result.  The odds are astronomically low that you could have both been infected and have a false negative test result at 3 months.

[empgraph]

Hello again, Doctor. It's 3 months since the single exposure with condom brokem that I describe above. It has been the only one, with a sex worker.

All of the tests that I describe were negative (21 days, 2 months), as you see, but just to do it "well" I waited and reached the 3 month mark. I took an ELISA test after 13 weeks and it was Negative, again.

In the last days, I felt with something like flu, headache, sore throat, etc. I know that symptoms are not indicative, so my question (I promise it is the final one) is: you are an experieced doctor in HIV, and I supose that you know some other colleagues who work with you. Have you EVER seen a 3-month negative test that later becomes positive in the 6 month mark or later?

I ask this because CDC says the tipical "97% will develop antibodies 3 months after...etc". OK, I assume that there isn't 100%-0% in medicine, BUT...97% is getting me mad! I understand 99% adter 3 months, but the "official" guideline means that 3 out of 100 people (like me) could be in a False Negative!!! And 3%, talking about HIV, is a lot.

So I don't understand this ultra-conservative guideline. That's why I consider your personal experience so important and I ask you that question.

THANK YOU VERY MUCH for your help.

[H. Hunter Handsfield, M.D.]

Numerical calculations are never completely reliable, but the chance you have HIV probably is far lower than that.  Your calculation is right if you know for sure your partner had HIV. If you assume that's a 1% chance, the likelihood you have HIV--assuming 90% test sensitivty at 3 weeks--is 0.01 x 0.0005 x 0.1 = 0.0000005, or one in 2 million.  That is 100 times less likely than your chance of dying tomorrow in an accident of some kind.  In other words, forget it.

[jv1977]

What about a high risk exposure and a 6 week negative test? Rare for that one to turn positive but I suppose it could happen.

[jv1977]

That's an interesting question. I wonder how often that does happen?  A negative 3 week test becoming positive at a later time (3 months)..........

[empgraph]

Thank you very much for your help, doctor. So, can we say that my odds are approximately 1/2000*10/100 (1 encounter and brief broken condom & 3 weeks Duo Test)??? That would be  a 99,99% probability that everything is OK. Do you agree? Have you ever seen or known cases like mine in which after a 3 week negative test they were positive in the 3 month mark?

Thanks a lot for all the good job you do here. Regards.