Clinical and Interpretive

This assay is used in the detection and diagnosis of chronic hepatitis C virus infection. A positive screening antibody test is reflexed to confirmatory PCR testing. Hepatitis C virus (HCV) is recognized as the cause of most cases of posttransfusion hepatitis and is a significant cause of morbidity and mortality worldwide. In the United States, HCV infection is quite common, with an estimated 3.5 to 4 million chronic HCV carriers.

Laboratory testing for HCV infection usually begins by screening for the presence of HCV antibodies (anti-HCV) in serum, using an FDA-approved anti-HCV screening test. Specimens that are repeatedly reactive by screening tests should be confirmed by more HCV-specific tests, such as direct detection of HCV RNA by reverse transcription-PCR (RT-PCR) or strip recombinant immunoblot assay (RIBA) using recombinant HCV-specific antigens.

HCV antibodies are usually not detectable during the first 2 months following infection, but they are usually detectable by the late convalescent stage (>6 months after onset) of infection. These antibodies do not neutralize the virus and they do not provide immunity against this viral infection. Loss of HCV antibodies may occur in the year following resolution of infection.Current screening serologic tests to detect antibodies to HCV include EIA and chemiluminescence immunoassay. Despite the value of serologic tests to screen for HCV infection, several limitations of serologic testing exist:
-There may be a long delay (up to 6 months) between exposure to the virus and the development of a detectable HCV antibody
-False-reactive screening test result can occur
-A reactive screening test result does not distinguish between past (resolved) and present HCV infection
-Serologic tests cannot provide information on clinical response to anti-HCV therapy

Reactive screening test results are followed by a supplemental or confirmatory test, such as RIBA for HCV antibodies or a nucleic acid test for HCV RNA. Nucleic acid tests provide a very sensitive and specific approach for the direct detection of HCV RNA.

A negative screening test result does not exclude the possibility of exposure to or infection with HCV. Negative screening test results in individuals with prior exposure to HCV may be due to low antibody levels that are below the limit of detection of this assay or lack of reactivity to the HCV antigens used in this assay. Patients with acute or recent HCV infections (<3 months from time of exposure) may have false-negative HCV antibody results due to the time needed for seroconversion (average of 8 to 9 weeks). Testing for HCV RNA (HCVQU / Hepatitis C Virus [HCV] RNA Detection and Quantification by Real-Time Reverse Transcription-PCR [RT-PCR], Serum) is recommended for detection of HCV infection in such patients.

This test profile is not useful for detection or diagnosis of acute HCV, since HCV antibodies may not be detectable until after 2 months following exposure and HCV RNA testing is not performed on specimens with negative anti-HCV screening test results. Initial testing for HCV RNA (HCVQU / Hepatitis C Virus [HCV] RNA Detection and Quantification by Real-Time Reverse Transcription-PCR [RT-PCR], Serum) is recommended for detection of HCV infection in such patients.

A single negative HCV RNA test result together with a reactive HCV antibody screen result with a S/CO ratio of ≥8.0 do not rule out the possibility of chronic HCV infection. Repeat testing for HCV RNA in 1 to 2 months is recommended in patient at risk for chronic hepatitis C.

Infants born to HCV-infected mothers may have false-reactive HCV antibody test results due to transplacental passage of maternal HCV IgG antibodies. HCV antibody testing is not recommended until at least 18 months of age in these infants.