The specificity of anti-HCV supplementary assays.

A total of 920 samples from blood donors screened as anti-HCV negative by two third-generation screening assays (Ortho Diagnostics v3.0 and Murex Diagnostics VK48) were tested by two supplementary anti-HCV assays, RIBA III (Ortho Diagnostics) and Western blot (Murex Diagnostics VK68). Six (0.65%) of the samples gave scorable bands by RIBA III and 5 (0.54%) by Western blot. Only single-band reactivity was seen and there was no consensus reactivity between the two assays. Single-band reactivity in supplementary assays, especially in samples from low-risk populations, needs to be interpreted with care before being taken as indication of genuine previous or current HCV infection.