Performance of VIDAS® anti-HCV as a second-line test for the detection of anti-HCV antibodies

OBJECTIVES:Detection of specific antibodies is crucial for routine diagnosis of Hepatitis C virus (HCV) infection. Nowadays, many commercial tests based on chemiluminescence technology are available as highsensitive screening methods. In case of weak reactivity on first-line assays, further investigations are required to discriminate true-positivity from biological false-positivity. For this purpose, immunoblot tests are used due to their highest specificity. Nonetheless, final interpretation problems and unsatisfactory cost-effectiveness strongly limit their usefulness in daily practice. In this study, we evaluated the performance of VIDAS® Anti-HCV (bioMérieux) as a second-line test for the detection of anti-HCV antibodies in order to limit the use of immunoblot in our laboratory setting. As preliminary data, we report on the concordance of VIDAS® Anti-HCV with RecomLine HCV IgG(Mikrogen) in a group of selected sera. METHODS: In our laboratory testing for anti-HCV antibodies was first performed on ARCHITECT Anti-HCV (Abbott), a full-automated, high throughput chemiluminescent assay. Sera were scored as positive or negative on the basis of signal/cut-off result (cut-off=1). In case of weak positivity and in certain clinical or epidemiological settings, further tests based on a different technology were performed to clarify doubtful results. Until June 2012, a second-line test based on enzyme-linked immunoassay (INNOTEST® HCV Ab IV, Innogenetics) was used. From July 2012, INNOTEST® HCV Ab IV was replaced by VIDAS Anti-HCV, a third-generation test combining a two-step enzyme immunoassay with a final fluorescent detection. Discordant results were arbitrated by RecomLine HCV IgG, a line immunoassay forqualitative antibodies detection against individual HCV antigens. To evaluate the performance of VIDAS® Anti-HCV, we compared the total amount of immunoblot assays performed during the year before and after the introduction of this new second-line test, in respect to the number of screening tests on ARCHITECT Anti-HCV. The concordance of VIDAS® Anti-HCV with RecomLine HCV IgG was calculated testing a panel of 127 sera with a s/co result ranging from 0.7 to 7.0 on ARCHITECT Anti-HCV assay. RESULTS: During the year before VIDAS® Anti-HCV introduction (July 2011-June 2012) a total of 634 immunoblot assays were performed. On the other hand, after its introduction (July 2012-June 2013) only 404 immunoblot tests were used as confirmatory method. Considering the total amount of anti-HCV screening tests, we noticed a significant decrease of cases requiring immunoblot from 7.5‰ (634/83802) to 4.8‰ (404/83769). Among selected sera, VIDAS® Anti-HCV showed a concordance with RecomLine HCV IgG of 73% (93/127). Border-line results of RecomLine HCV IgG were considered as positive. CONCLUSION: In our experience, VIDAS® Anti-HCV showed a good diagnostic performance as second-line test for anti-HCV antibodies detection, limiting the use of immunoblot tests.