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DNA PCR false positive
Oct 27, 2007

Dear Dr. Conway- I've been able to find information on the reasons for false negative DNA PCR tests, but nothing on what can cause a false positive. (But everyone warns that they're not used as often because of false positives.) Could you please give a bit of information on what can cause false positives and if possible, some information on how the test results are presented? Is it simply "not detected" or "detected". And how is a false positive ruled out?

Thank you!

Response from Dr. Conway

The DNA test currently used in clinical practice is a qualitative test, which is reported as either positive or negative. It can be falsely negative if there is a very small amount of DNA that is present, or if there is something in the sample that prevents the PCR test from working well. Both of these eventualities are quite rare. It can be falsely positive if there is a mix-up with the sample, if the sample is contaminated or, rarely, if there is something other than HIV that is being detected. In the latter case, it will usually be a very "weak" positive result, which should give us a clue to do further testing before concluding that infection is present. In all cases, if the positive test result is felt to be unexpected, it should be confirmed by some other HIV test before concluding that infection is present.

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