Four virological markers of hepatitis C virus (HCV) infection are used clinically for management of patients with hepatitis C, namely the HCV genotype, HCV RNA, HCV core antigen, and antibody to HCV (anti-HCV). The diagnosis of acute and chronic hepatitis C is based on both anti-HCV detection using enzyme immunoassays (EIA) and HCV RNA detection using a sensitive molecular biology-based technique. Other virological tools, including HCV genotype determination and HCV RNA quantification, are now used to tailor treatment to the individual patient and to determine its efficacy. This article reviews the kinetics of HCV markers during acute and chronic HCV infection, together with current assays and their practical use in the management of HCV-infected patients. (HEPATOLOGY 2002;36: S65-S73.) irological diagnosis and monitoring of hepatitis C virus (HCV) infection are based on 2 categories V of laboratory test, namely serologic assays detecting specific antibody to HCV (anti-HCV) (indirect tests) and assays that can detect, quantify, or characterize the components of HCV viral particles, such as HCV RNA and core antigen (direct tests). Direct and indirect virological tests play a key role in the diagnosis of infection, therapeutic decision-making, and assessment of the virological response to therapy.
Virological Assay Techniques
Immzrnoenzymatic Techniques
Immunoenzymatic techniques are widely used to detect and, sometimes, to quantify viral antigens or specific antibodies in body fluids.
Enzyme Immunoassays. In enzyme immunoassays (EM) or enzyme-linked immunosorbent assays (ELISA), serum or plasma antibodies or viral antigens are captured on the wells of microtiter plates by using the corresponding antigen or specific (generally monoclonal) antibodies, respectively. Antigen-antibody complexes are then specifically revealed in a colorimetric enzymatic reaction. After reading in a spectrophotometer, the result is expressed as the ratio of the optical density of the test sample to that of a kit control. EIAs are easy to use, partly or fully automated, and suitable for testing large numbers of samples.
Immunoblot Assays. Immunoblot tests also detect specific antibodies, but using viral antigen-coated nitrocellulose strips instead of microtiter plates. Positive reactions are characterized by the appearance of colored bands at specific positions on the strip.' Interpretation may be visual or automated.