Improved efficiency of national HIV, HCV, and HTLV antibody testing algorithms based on sequential screening immunoassays

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Abstract
Traditional strategies for clarifying the antibody status of donors giving repeatedly reactive (RR) results on primary screening immunoassays (IA1) have usually involved direct testing by immunoblot. However, such strategies can generate nonspecific in determinate results. The aim of this report is to present the results of an alternative strategy based on the use of sequential immunoassays (SI) before immunoblot testing. The efficiency of traditional and SI strategies was compared in terms of the number of IA1 RR samples requiring immunoblot testing and the percentage of immunoblot tests giving indeterminate results. In addition, the biologic false- reactive overlap between the PRISM assays selected as IA1 and candidate secondary screening immuno- assays (IA2) was calculated to determine the most efficient IA1/IA2 combinations. There was a significant decrease in the proportion of IA1 RR samples requiring immunoblot testing under the SI strategy when compared with existing site-specific strategies for HIV (0.49 vs. 0.08, p < 0.05), HCV (0.85 vs. 0.42, p < 0.05), and HTLV (0.69 vs. 0.05, p < 0.05) algorithms. In addition, there was a significant decrease in the percentage of immunoblot tests giving indeterminate results for HIV and HTLV under the SI strategy. However, there was no significant difference in the proportion of confirmed positive results for HIV, HCV, or HTLV before and after national SI algorithm implementation. For the anti-HIV IA2s, there was considerable variation of biologic false-reactive overlap with the PRISM HIV O plus chemiluminescent immunoassay (range, 1.6-15.6%). The results presented in this report demonstrate that the sequential use of screening immunoassays before immunoblot testing can significantly reduce both the number of immunoblot tests and proportion of indeterminate results, without impacting sensitivity, thereby improving algorithm efficiency and simplifying donor management.