Indeterminate results of the second-generation hepatitis C virus (HCV) recombinant immunoblot assay: significance of high-level c22-3 reactivity and influence of HCV genotypes.

A second-generation recombinant immunoblot assay (RIBA 2.0) is used in the United States to confirm infection with hepatitis C virus (HCV) in samples that are anti-HCV (enzyme immunoassay) positive. In some cases, indeterminate results of RIBA 2.0, which are defined as reactivity to a single antigen species or reactivity limited to two proteins derived from the same coding region of the HCV genome, are encountered. This study was performed to establish the significance of indeterminate RIBA 2.0 results in relation to HCV RNA detection, high positivity for the c22-3 band, and the HCV genotype as determined by direct DNA sequencing. Ninety-six samples with indeterminate RIBA 2.0 results were studied. HCV RNA was detected in 21 of 34 (62%) samples with high reactivity to c22-3 and in 8 of 62 (13%) samples with low reactivity to c22-3. The HCV genotype distribution in samples that were RIBA 2.0 indeterminate and HCV RNA positive was significantly different from that in samples of a control group with positive results for both the RIBA 2.0 and HCV PCR. These results suggest that highly positive c22-3 samples are likely to be associated with HCV viremia and that infection with less common HCV genotypes is more commonly associated with indeterminate RIBA 2.0 results.