Use of third-generation hepatitis C virus (HCV) enzyme immunoassay (EIA) to resolve second-generation HCV EIA-reactive and second-generation recombinant immunoblot assay-indeterminate blood samples: data to support current Food and Drug Administration guidance on HCV lookback

In considering a proposed role for HCVEIA 3.0 in resolving the lookback status of HCV EIA 2.0-RR/RIBA 2.0-indeterminate donations, two critical questions must be considered. The first of these questions is: What is the probability that a nonreactive HCV EIA 3.0 result in such samples will result in misclassification of an infected donation as negative, precluding lookback that would have been triggered had RIBA 3.0 been performed as recommended by the draft guidance document? In the studies reviewed above, a total of 325 HCV EIA 2.0-RR/RIBA 2.0-indeterminate donations tested HCV EIA 3.0- nonreactive and were further tested by RIBA 3.0 and, in most cases, for HCV RNA by PCR or TMA (Table 3). Two (0.6%) of these sample tested RIBA 3.0- positive; one of these was indeterminate on repeat RIBA 3.0 testing and both were negative for HCV RNA. We believe this low rate of RIBA 3.0 positivity and the absence of HCV RNA positivity support a recommendation that further testing and lookback are not warranted on HCV EIA 3.0-nonreactive donations. The second question is: What is the probability that a reactive HCV EIA 3.0 result on such samples will be corroborated by a positive RIBA 3.0 result that would justify lookback? Before performing the present study on HCV EIA 2.0-RR/RIBA 2.0-indeterminate donations, we predicted that the rate of RIBA 3.0 positivity among HCV EIA 2.0-RR/RIBA 2.0-indeterminate donations that were further tested and found to be HCV EIA 3.0-reactive would be similar to the 75-percent rate observed among HCV EIA 3.0-reactive/RIBA 2.0- indeterminate donations. If this were confirmed, we felt it would be reasonable to trigger lookback on the basis of the reactive HCV EIA 3.0 results, as is currently being done for prospectively identified HCV EIA 3.0- RR/RIBA 2.0-indeterminate donors. In the pilot study, we found that only about 30 percent of HCV EIA 2.0-RR/RIBA 2.0-indeterminate donations that tested HCV EIA 3.0-reactive were RIBA 3.0 positive. A likely explanation for this discrepancy is that, during the several years of testing donors with an HCV EIA 2.0, donors with 'false-positive' reactivity, characterized by concordant HCV EIA 2.0 and HCV EIA 3.0 reactivity and indeterminate RIBA 2.0 results, were identified and deferred (i.e., removed from the donor base). Consequently, the likelihood (predictive value) that a donation with an RR HCV EIA 3.0 and indeterminate RIBA 2.0 will test RIBA 3.0-positive is greater among current HCV EIA 3.0-RR donors than during the initial period of HCV EIA 2.0 screening. In light of this relatively low rate of RIBA 3.0 positivity among HCV EIA 3.0-reactive samples identified among retrospective HCV EIA 2.0-RR/RIBA 2.0-indeterminate donations we do not believe that triggering lookback on the basis of positive HCV EIA 3.0 results alone is justified. Further testing of these samples by RIBA 3.0 is strongly recommended.