As mentioned earlier, for those with chronic HCV, NAAT testing (or viral load testing) is used to monitor the patient's response to treatment. However, the initial diagnostic test for HCV begins with antibody testing. HCV Ab testing assesses specific anti-HCV IgG. HCV IgG antibodies are usually not detectable during the first 2 months after infection, but are detectable by the late convalescent stage (around 6 months after onset of infection).
The reason HCV IgM antibodies are not routinely tested is because the window of time in which anti-HCV IgM is made is short with HCV. In addition, many with HCV are asymptomatic at first, and thus, by the time they present to a clinician their IgG titers are high and thus serve as a more useful marker. A negative Hep C Ab test on the acute viral panel suggests the patient is not currently infected with HCV. If this assay is 'reactive' or positive, it suggests the patient has at least been exposed with HCV but it does not necessarily prove current HCV infection since a person who has cleared an HCV infection will have life-long titers of anti-HCV antibodies in their serum.
If an HCV serology test is positive, most laboratories will automatically reflex testing for HCV RNA. If NAAT comes back positive, then the patient is confirmed to be viremic (i.e. they have active an infection). If NAAT comes back negative, then it is presumed that the patient was exposed to HCV but has cleared the virus. For the CDC's interpretation of HCV test results, view the image or visit this
link.
