Laboratory Diagnosis of HCV Infection
Abstract & Commentary
Synopsis: Either a sensitive test for HCV RNA or a recombinant immunoblot assay (RIBA) may be used to confirm the presence of HCV infection in an individual with a positive screening test.
Source: CDC. Guidelines for laboratory testing and result reporting of antibody to hepatitis C virus. MMWR Morb Mortal Wkly Rep. 2003;52:1-16.The CDC has updated their guidelines regarding the performance and interpretation of testing for the presence of hepatitis C virus (HCV) infection. Although primarily directed at laboratories, their recommendations are also useful to the clinician.
Two enzyme immunoassays (Abbott HCV EIA 2.0 and ORTHO HCV Version 3.0 ELISA) and 1 enhanced chemiluminescence immunoassay (VITROS Anti-HCV assay) have received FDA approval for use as screening tests in the detection of HCV infection. Although the specificity of these screening tests is > 99%, when applied to immunocompetent populations with anti-HCV prevalences < 10%, the false-positivity rate averages 35%. As a consequence, positive results with these tests require confirmation by a supplementary test—either a strip immunoblot assay (Chiron RIBA HCV 3.0 SIA) or a nucleic acid test (AMPLICOR Hepatitis C Virus Test, version 2.0 or COBAS AMPLICOR Hepatitis C Virus Test). Both nucleic acid tests have a lower limit of detection of approximately 50 IU/mL.
Falsely negative RIBA tests may occur during the first weeks after infection (the "window period"), and seroconversion rarely can be delayed for months. Persistent false-negative tests may occur in some immunocompromised patients. Indeterminate RIBA results may occur during the process of seroconversion and also in an occasional patient with chronic HCV infection. The meaning of an indeterminate RIBA may be clarified by repeating the test after an interval of at least 1 month or by testing for the presence of HCV RNA.
A positive screening test may also be confirmed by HCV RNA testing. Patients with a positive screening assay and a negative assay for HCV RNA should undergo testing by RIBA. If the latter is also negative, the patient is considered to not be HCV-infected. If the RIBA is positive and HCV RNA is undetectable, the patient may have resolved the infection. Alternatively, this pattern may represent a temporary result in some patients during acute, as well as during chronic, infection. Thus RIBA-positive, HCV RNA-negative patients should have follow-up testing.
Comment by Stan Deresinski, DM, FACP
These recommendations provide a straightforward set of guidelines for the interpretation of laboratory testing in suspected HCV infection. Perhaps the most difficult areas in clinical practice are dealing with the delay in seroconversion after acute infection and the recognition of false-positive antibody tests in some immunocompromised patients.
The average window period from infection to seroconversion is reported to be approximately 70 days.1 One nucleic acid assay (not one of those mentioned above) reduced that period by an average of 26 days.1 An ELISA test for HCV core antigen is reported to have similar benefit.2
Patients undergoing maintenance hemodialysis may have falsely negative HCV antibody tests. This was true of 5% of 238 seronegative patients in a German study.3 In another study, 22% of HCV RNA patients were antibody negative.4
Dr. Deresinski is Clinical Professor of Medicine, Stanford; Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center
References
1. Kolk DP, et al. Significant closure of the human immunodeficiency virus type 1 and hepatitis C virus preseroconversion detection windows with a transcription-mediated-amplification-driven assay. J Clin Microbiol. 2002;40:1761-1766.
2. Icardi G, et al. Novel approach to reduce the hepatitis C virus (HCV) window period: Clinical evaluation of a new enzyme-linked immunosorbent assay for HCV core antigen. J Clin Microbiol. 2001;39:3110-3114.
3. Schroter M, et al. High percentage of seronegative HCV infections in hemodialysis patients: The need for PCR. Intervirology. 1997;40:277-278.
4. Hinrichsen H, et al. Prevalence and risk factors of hepatitis C virus infection in haemodialysis patients: A multicentre study in 2796 patients. Gut. 2002;51: 429-433.
Synopsis: Either a sensitive test for HCV RNA or a recombinant immunoblot assay (RIBA) may be used to confirm the presence of HCV infection in an individual with a positive screening test.Subscribe Now for Access
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