Molecular Diagnostics Used for Hepatitis C Virus Infection

Hepatitis C virus (HCV) is a common blood-borne pathogen that relies heavily on nucleic acid testing for confirmation of infection. A review of the currently available molecular diagnostic tests for HCV, their clinical applications, and how these tests shed light on the natural history of HCV has appeared in the February 2007 issue of the Journal of the American Medical Association (JAMA).

Qualitative nucleic acid tests have low limits of detection--<50 international units (IU) HCV RNA/ml--and are used for confirmation of HCV infection and for screening blood donations. HCV 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 virologic response is defined as testing negative for HCV RNA six 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 four weeks of therapy constitutes a rapid virologic response and is a strong predictor of treatment success. Patients who have not had an early virologic response, defined as at least a two-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.

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 virologic response. The same type of quantitative HCV RNA test should be used throughout a patient's treatment course.

The authors of the review were John D. Scott, M.D., M.Sc., department of medicine, division of allergy and infectious diseases, and David R. Gretch, M.D., Ph.D., and departments of laboratory medicine and medicine, University of Washington (Seattle, WA, USA).


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