Oct 15, 2012
Hello, in UK most hospitals offer a quick test based on finger prick. They say that it gives false positives in 7 cases out of 1000. My exposure was (I believe) quite low, because it was a condom breakage during vaginal intercourse with an italian 35 year old woman (not a pro) of unknown status. I felt the breakage and immediately pulled off. At the hospital they say that in case of a positive (reactive) result from the test they repeat it. My question is: what is the reason for a false positive? It has to do with the test equipment, or can it be due to the way the doctor/nurse performs it? Because clearly if the latter is true then the false positive is a human error, and it is possible that also the second test will be a false positive (because for example the person is inexperienced, which I would not be surprised considering the service provided by the British NHS). I understand the question might look silly, but in the past I had some blood tests consisten with leucemia which turned out to be completely wrong. I know how stressing it is to get a positive test, even one than later turns out to be false positive, and I would rather avoid going trough something like that again. thanks
Response from Dr. Wohl
HIV screening tests are designed to be sensitive, that means they are supposed to be very good at picking up almost all true infections. To accomplish that, the test accepts that some of what it detects may not be HIV at all but something else. But, the idea is that it is better to overcall HIV than under-call it. So, this is not user error. In fact human error can increase false negative results (this is why home based tests are not as accurate as those done by clinics or trained staff).
The confirmatory HIV testing is specific, that is designed to identify antibodies to HIV, even if that means undercalling the close calls.
Hope this makes sense.
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