hi dr, have a good day. I've read in one UK HCV guidelines, that if you are faced with an isolated incident of exposure to HCV blood (infected, or strongly suspected of being infected, with HCV), you should get tested for HCV RNA testing at 6, 12 and 24 weeks and anti-HCV testing at 12 and 24 weeks.my question is that: why these time frames are being selected, does the virus only appears in blood and becomes detectable at these times, what happens if you got tested outside these time frames and you are negative more than once. thank you for your kinddness

I would say that guidelines do vary in the testing algorithms because these are only educated guesses.

However, testing for both RNA and antibody as far out as 24 weeks seems expensive to me without clear benefit. After exposure, the vast majority of persons acquire virus in their blood in 2 to 6 weeks and seroconversion occurs by about 12 weeks. Of course, there is a small percentage of persons who seroconvert later so antibody testing at later time points is certainly reasonable at 24 weeks. I would not personally recommend RNA testing at 24 weeks.