Reliability of PCR testing after PEP
Posted: Jul 21, 2007
QUESTION:
Dear Dr. Young, Quick question: A HCW had a needlestick injury involving a pt of known HIV/HepC status in mid April and was then treated with Combivir/Tenofovir for 4 weeks for this exposure. She has had an 8wk ELISA test (neg) on June 11th (4wks after completion of PEP) and a 9wk RNA-PCR test(not-detected) on June 16th (5wks post completion of PEP)for some non-specific symptoms. She is still very anxious about this and having a hard time foucusing on her work. Can you tell me about the reliabilty of these test ? Are they reassuring or not really ? What is the BEST timeline for further testing to definitively rule out the possibility of infection(given that the pt was on PEP for the 1st 4wks)? Thanks in advance for writing back. -RT
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RESPONSE FROM: 
Dear RT,
Thanks for your post.
While not formally approved to diagnose (or rule out ) HIV infection, I'd find that the RT-PCR viral load tests to be a very reliable way to detect HIV. If anything, the test is too sensitive (hence, potentially raising the false negative rate).
So, for your patient, a negative PCR at week 9 should be highly reassuring. There isn't clear guideance on the use of PCR regarding timelines, but if the test remains negative 8 weeks after stopping PEP, I'd feel very good about your patient's prognosis. In any event, I'd still recommend doing antibody testing at 3, and probably 6 months after exposure (depending of course on your local standard of care).
Hope this is helpful, BY
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