Reliability of the third-generation recombinant immunoblot assay for hepatitis C virus

In a confirmatory laboratory, the second-generation recombinant immunoblot assay (RIBA-2) was replaced by the third-generation RIBA (RIBA-3) in March 1993. The aim of this validation study was to compare the sensitivity and specificity of RIBA-2 and RIBA-3 in a routine setting, by using a validated hepatitis C virus (HCV) RNA polymerase chain reaction to establish plasma viremia.

RIBA-2 testing was performed (March 1991-March 1993) in 593 HCV RNA-positive and 1498 HCV RNA-negative subjects. RIBA-3 testing was performed (March 1993-May 1994) in 220 HCV RNA-positive and 530 HCV RNA-negative subjects. All samples reacted for anti-HCV in enzyme-linked immunosorbent assay.

In HCV RNA-positive individuals, the sensitivity of RIBA-3 was significantly higher than that of RIBA-2 (99.5% vs. 93.3%, p = 0.0005). This was not caused by inclusion of the NS5 antigen, but by a higher sensitivity of the antigens c33 and c100 (RIBA-2: 94.3% and 62.6%; RIBA-3: 99.5% and 88.6%). Replacement of the c22 and c100 recombinant proteins by synthetic peptides significantly reduced nonspecific reactivity against these antigens (p < 0.0001). Unfortunately, increased nonspecific reactivity against the modified c33 antigen and the new NS5 antigen canceled out this effect. Two-band reactivity occurred more often in nonviremic persons than in viremic persons (32.7% vs. 8.2%, p < 0.0001). Risk factors for HCV infection were less frequently observed in 11 blood donors with two-band reactivity than in 6 blood donors with other positive RIBA-3 patterns (18% vs. 83%, p = 0.03).

The higher sensitivity of RIBA-3 significantly reduced the number of indeterminate test results in HCV RNA-positive persons. Confirmatory laboratories must be aware of the frequent occurrence of nonspecific, isolated reactivity and even nonspecific, two-band reactivity in anti-HCV enzyme-linked immunosorbent assay-reactive blood donors.