DNA PCR Testing - Question - Anyone know the answer to?

I am reading around the forum about DNA PCR question and I am kind of confused....

I took a HIV DNA PCR from Labcorp (http://www.areuatrisk.com) and they claim you need to be post 28 days of exposure ( i took it at day 40).  Reading some posts from the doc, I see people getting PCR prior to 28 days.  Does PCR lose its affectiveness after 28 days -or- is it just that a normal antibody test would suffice for testing that late? Either way I had both standard antiboy ELISA and DNA PCR - both negative at 40days.  Labcorp says that no further testing is needed

(FYI exposure was 1 time unprotected vaginal sex with a female friend of mine (who says she is HIV negative)).  

Anyway, I see a lot of don't get PCR testing on the boards, and I was just curious as to why?

Thanks

[peekawho]

PCR tests have an uncomfortably high rate of false positives, which would lead to incredible anxiety as you can imagine.  If all your tests were negative and you had a low risk exposure (as you did) you are fine.

[Anxious and Worried]

DNA PCR Testing is 100% conclusive after 28days.  Most people will have HIV DNA in their blood within 72 hours after exposure.  This test is not FDA approved mainly due to the cost but it is widely regarded as one of the top tests out there.

[Anxious and Worried]

Pretty much according to info about the test and after speaking with counselors at the Medical Testing Center ( www.medicaltestingcenter.com )

[ScaredinUSA]

So you are saying that post 28 days - this test being negative would say 100% HIV negative?  Well thats awesome to hear!

[Tommy420]

Hi ScaredinUSA. The DNA PCR test isn't recommended for two reasons: (1) it is definitely conclusive after 28 days, however most people will have developed antibodies after 28 days, so a regular antibody test would be positive anyway. (2) It is expensive.

If a person was indeed exposed to HIV and acquired the virus, the DNA PCR test would be 100% positive after 28 days, even if you tested at 40 days, or 4 years later. It would always show positive once you were infected. However, that would not necessarilly be the case for a RNA PCR, which actually measures the viral load. Hope that helps.

YOu are 100% HIV negative. If you're still concerned, wait 12 weeks and take another test so you don't have to stress yourself over it anymore.

[Tommy420]

I forgot to add that DNA PCR tests also have a high rate of false positivity due to their extra sensitivity!