Hepatitis C virus (HCV) is a common blood-borne pathogen that relies heavily on nucleic acid testing for confirmation of infection. Nucleic acid tests are invaluable for the diagnosis of HCV infection and provide critical prognostic information for guiding treatment and measuring the response to antiviral therapy.Objective
To review the currently available molecular diagnostic tests for HCV, their clinical applications, and how these tests shed light on the natural history of HCV.Evidence Acquisition
Search of MEDLINE (1966 to July 2006), article reference lists, and national meeting abstracts for the diagnosis and applications of molecular diagnostic tests for HCV. Studies were selected on the basis of clinical relevance.Evidence Synthesis
Qualitative nucleic acid tests have low limits of detection (<50 IU HCV RNA/mL) and are used for confirmation of HCV infection and for screening blood donations. Hepatitis C virus genotype test results provide important prognostic information related to therapeutic response and are routinely used for selecting treatment regimens. Quantitative HCV RNA testing provides prognostic information regarding likelihood of treatment response and plays an important role in monitoring the antiviral response to treatment. Sustained virological response is defined as testing negative for HCV RNA 6 months after cessation of therapy. Recent studies suggest that the rate of response to therapy is also important. For example, conversion to an HCV RNA negative test result after 4 weeks of therapy constitutes a rapid virological response and is a strong predictor of treatment success. Patients who have not had an early virological response, defined as at least a 2-log decline in HCV RNA after 12 weeks of therapy, are unlikely to respond with an additional 36 weeks of therapy, and should stop therapy.Conclusions
A sensitive nucleic acid test should be used to confirm all cases of acute or chronic HCV infection. A genotype test and quantitative HCV RNA test should be performed on all patients prior to therapy to best assess probability of response and to aid in selection of appropriate therapeutic regimen. Monitoring HCV RNA during treatment provides important information on likelihood of sustained virological response. The same type of quantitative HCV RNA test should be used throughout a patient's treatment course.