Specificity and sensitivity of first and second generation anti-HCV ELISA in a low prevalence population

Specificity and sensitivity of the second generation enzyme immunosorbent assay for hepatitis C antibodies were calculated from data on 208,554 blood donors screened with either the first or the second generation tests (ELISA I, ELISA II) or both (4,639 donors). The second generation ELISA was no more specific than the first generation test in this low-prevalence blood donor population (specificity 99.7% vs 99.6%). Most of the donors (93.5%) who were found to be reactive using ELISA II were negative or indeterminate according to a supplemental test, the second generation recombinant immunoblot assay (RIBA II). The second generation ELISA was found to be more sensitive than the first. It identified all 16 donors who were positive according to RIBA II during screening with ELISA I. The latter found only 13 out of 30 donors (43%) who were positive according to RIBA II during screening with ELISA II. If the number of RIBA II positive donors found during the first year of screening with ELISA I (74, 0.024%), and the number of RIBA II positive but ELISA I negative donors found during screening with ELISA II, are taken into consideration it can be estimated that the added sensitivity due to using ELISA II is about 40%.