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BACKGROUND: A variety of laboratory tests are available to diagnose hepatitis C virus (HCV) infection. Commonly, an enzyme immunoassay (EIA) for anti-HCV antibodies is performed as an initial screening test. If the screening EIA is positive, additional testing is required to confirm disease. Confirmatory tests, according to the CDC case definition for hepatitis C, include the EIA signal to cut-off ratio, the recombinant immunoblot assay (RIBA), and nucleic acid testing (NAT) for HCV RNA. We examined trends in use of HCV diagnostic tests among cases of confirmed hepatitis C reported in Pennsylvania between 2003 and 2010.
METHODS: Information on laboratory tests reported to the Pennsylvania Department of Health’s reportable disease surveillance system on confirmed cases of hepatitis C was obtained for the years 2003 to 2010. The types of tests and the order in which they were performed were determined on a per-case basis.
RESULTS: From 2003 to 2010, 73,608 confirmed cases of hepatitis C were reported. For 78% of these, positive HCV screening EIA tests were received. Signal to cut-off ratios were reported for 0.8% of cases in 2003 and 11.7% cases in 2010. RIBA tests were used to confirm 8.4% of cases in 2003, and 9.1% of cases in 2010. HCV RNA tests were used as a confirmatory method for 39.7% and 49.2% of cases in 2003 and 2010 respectively. The percentage of cases with positive NAT tests not preceded by EIA screening testing decreased from 42.6% in 2003 to 27.7% in 2010. The mean time between first reported positive EIA and first reported positive NAT decreased from 1,113 days in 2003 to 101 days in 2010.
CONCLUSIONS: Although reporting of EIA signal to cut-off ratios increased substantially from 2003 to 2010, only a small proportion of HCV cases were confirmed using this method. Use of RIBA tests has remained relatively stable. NAT is being used more frequently as a confirmatory test for hepatitis C; it also appears that NAT is being used as a primary test in some cases. The mean time between first positive EIA and NAT test has decreased over the last 8 years. Since NAT testing is often used to monitor progression of hepatitis C disease and efficacy of treatment, use of NAT testing might serve as a proxy indicator for linkage to care for hepatitis C patients.