The diagnostic efficacy of Ortho VITROS chemiluminescence assay (CIA) in detecting antibodies to the hepatitis C virus (HCV) and the clinical significance of specimens with low sample-to-cut off (S/Co) ratio was analysed, comparing the positive rate for CIA in 5,550 consecutive outpatients with enzyme-immunoassay (EIA). In parallel testing, 43 samples (0.8%) were low positive by CIA (S/Co ratio from 1.0 to 8.0) but negative by EIA. No samples CIA negative/EIA positive were found. Among EIA negative results we found 22 RIBA positive or indeterminate, yielding CIA sensitivities of 100% and EIA sensitivity of 97.8%. None of the 33 samples with CIA S/Co ratios of ≤ 2.0 and only 3 (10.7%) with S/Co ratios of between 2.1 and 8.0 were found to be RIBA positive. Instead, the majority of samples with S/Co ratios ≤ 8.0 (55.7%) were recombinant immunoblotting assay (RIBA) negative. HCV RNA and/ or clinical evidence of HCV infection was not found in any of the 12 indeterminate cases examined with S/Co ratios ≤ 2. We suggest to report them as “Borderline”, with the recommendation to follow up in the future.
Key words: HCV infection, RIBA, HCV-RNA, CIA, EIA.
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