Hi docs,

Are the HIV and Hep C PCR tests determinative (and if so when post exposure)? 

Or if not determinative when do you need to follow up with antibody tests post exposure to be sure of result?

Thank you!

Hepatitis C virus is almost never sexually transmitted. There is no sexual risk except for potentially traumatic rectal sex between men who have sex with men, and even then the risk is low. Since hep C is not an STD, we are not experts in HCV testing and have little experience with it. In general, PCR for HCV RNA is done only in persons who test positive for antibody, to distinguish between actual infection and past infection that has been cured. It is not normally done after a particular exposure. If the test is used in that way, it usually would be positive within 2 weeks; a negative result after that would be some reassurance that infection didn't happen, but later antibody testing after 8-12 weeks also should be done.

The HIV PCR test is almost always positive by 11-12 days after exposure in newly infected persons, and for sure by 14 days. However, to be maximally safe most experts advise another test -- preferably an antigen-antibody test (AgAb test, "4th generation") 6 weeks after exposure.

I might be able to help more if you'd like to say what sort of exposure(s) you have had. In the meantime, I hope these comments are helpful. 

HHH, MD