Performance of parallel screening of Brazilian blood donors with two human immunodeficiency virus immunoassays: implications for sequential immunoassay testing algorithms in other countries

In Brazil it is mandatory to screen donors for human immunodeficiency virus (HIV) antibodies using two immunoassays (IAs) in parallel. Confirmatory testing is performed only on reactive donors who return for counseling. The goal of this analysis was to determine if concordant IA reactivity accurately predicts infection and can be used for HIV incidence and/or prevalence analyses.

We reviewed HIV screening and confirmatory results obtained for 307,407 donations in the first year of the REDS-II study in Brazil (2007) and for 2,304,755 donations collected from 1996 to 2006 in one of the REDS-II sites (São Paulo, Brazil).

In the São Paulo site, 11,410 (0.50%) HIV IA-reactive donations were discarded, but only 2095 (0.09%) were reactive to both IAs. Western blot was positive on 1002 (48%) dual-IA-reactive donors who returned for counseling. Only four HIV-infected donors were detected who had been missed at screening by one of the IAs; all occurred before 2002. The positive predictive value (PPV) of dual-IA reactivity varied from 45.8 to 100%, with 80% to 90% PPVs when using IAs from different manufacturers. If both assays yielded signal-to-cutoff (S/C) values of 3.0 or more, PPVs ranged from 91% to 99%, with approximately 99% sensitivity for true HIV seropositivity.

Parallel testing of all donations has limited efficacy when highly sensitive IAs are used. Reactivity by two sequential IAs is useful for prevalence studies if the assays are from different manufacturers and especially if high S/C values are considered.