HEPATITIS

HEPATITIS / YOUNOSSI

diagnostic tests Hepatitis C Since the HCV genome was cloned in 1989,²⁰⁴ the extensive use of molecular techniques has led to the development of serologic and molecular tests for detecting the virus and its subtypes, as well as to an increase in our understanding of the pathogenesis of chronic liver disease. Two categories of virologic assays are used for the diagnosis and management of HCV infection: serologic assays based on HCV immunologic characteristics and molecular-based assays based on the quantitation and characterization of the HCV RNA.^{192,193,205–208} Antibody tests in hepatitis C. Serologic assays include screening tests based on EIAs and immunoblot assays. Numerous serologic tests exist to detect antibodies to HCV antigens,^209,210 but the utility of these assays is limited by the observation that not all patients infected with HCV generate an immune response.^211–213 The ELISA has been the major screening test for the detection of anti-HCV against different HCV antigens. Supplemental semiquantitative assays developed to refine the specificity of a positive anti-HCV EIA assay include recombinant immunoblot assay (RIBA). The utility of RIBA testing is to decrease false positive ELISA tests that may still be seen in individuals with no apparent risk factors for HCV and those with other immune-mediated disease (eg, rheumatoid arthritis). In high-risk individuals, the positive predictive value of the ELISA-2 test is over 95% and in the presence of elevated ALT levels virtually establishes the diagnosis. HCV-RNA tests. Notably, serologic methods may fail to detect HCV infection in the small proportion of patients unable to mount an effective immune response. Additionally, although a positive antibody response to HCV generally indicates infection, it does not distinguish between active and previous infection and therefore is of no benefit in assessing recovery after antiviral treatment. In this context, identification of the presence of HCV RNA in serum or plasma is clearly more useful. Molecular assays for HCV include qualitative assays detecting HCV RNA in body fluids and liver biopsy specimens; quantitative assays measuring HCV viral load, a parameter that estimates the level of HCV replication; and tests analyzing the sequence of HCV genomes, or "genotyping" assays (see below).²⁰⁸ Sensitive qualitative tests for detection of HCV RNA in serum by reverse transcriptase (RT)-PCR or bDNA methods have been shown to be useful in the diagnosis of active HCV infection.^214–217 Accurate quantitative methods for measuring viral nucleic acid levels (ie, counting the number of viral particles) in patient serum have also been shown to correlate with the clinical stage of disease.
Volume 67 Supplement 1	Cleveland Clinic Journal of Medicine
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