Discordant human T-lymphotropic virus screening with Western blot confirmation: evaluation of the dual-test algorithm for US blood donations.

Abstract

Human T-lymphotropic virus (HTLV) blood donation screening has used a dual-testing algorithm beginning with either a chemiluminescent immunoassay or enzyme-linked immunosorbent screening assay (ELISA). Before the availability of a licensed HTLV supplemental assay, repeat-reactive (RR) samples on a first assay (Assay 1) were retested with a second screening assay (Assay 2). Donors with RR results by Assay 2 were deferred from blood donation and further tested using an unlicensed supplemental test to confirm reactivity while nonreactive (NR) donors remained eligible for donation until RR on a subsequent donation. This "dual-test" algorithm was replaced in May 2016 with the requirement that all RRs by Assay 1 be further tested by a licensed HTLV supplemental test (Western blot [WB]). In this study, we have requalified the dual-test algorithm using the available licensed HTLV WB. We tested 100 randomly selected HTLV RRs on screening Assay 1 (Abbott PRISM chemiluminescent immunoassay) but NR on screening Assay 2 (Avioq ELISA) by a Food and Drug Administration-licensed WB (MP Biomedicals) to ensure that no confirmed positives were among those that were RR by Assay 1 but NR by Assay 2. Of the 100 samples evaluated, 79 of 100 were WB seronegative, 21 of 100 indeterminate, and 0 of 100 seropositive. Of the 79 of 100 seronegative specimens, 73 of 79 did not express any bands on WB. We demonstrated that none of the 100 samples RR on Assay 1 but NR on Assay 2 were confirmed positive. This algorithm prevents such donors from requiring further testing and from being deferred.