Objective: To retrospectively compare the accuracy of combinations of two enzyme-linked immunosorbent assays (ELISAs) with a Western blot based strategy for identification of human immunodeficiency virus type 1 (HIV-1) seropositivity.
Materials and methods: 48,977 sera, sent to the National Bacteriological Laboratory, Stockholm, Sweden, for HIV antibody determinations between October 1988 and June 1993, were investigated. All samples were tested in parallel with two different ELISAs, either Abbott Recombinant HIV-1 EIA and Wellcozyme Recombinant Anti-HIV-1 EIA, or Enzygnost Anti-HIV-1/2 and Wellcozyme Recombinant Anti-HIV-1 EIA, or Enzygnost Anti-HIV-1/2 and Wellcozyme Anti-HIV-1+2 EIA. 1565 sera repeatedly reactive by one or both ELISAs were investigated by Western blot (WB). Furthermore, a total of 2820 referred sera, screen reactive at primary laboratories but negative on our combinations of two ELISAs were analysed by WB.
Results: Out of 1244 truly HIV antibody positive samples 1203 were WB positive and 41 (3.4%) were WB indeterminate. A sensitivity of 100% was obtained by all three combinations of two ELISAs on examination of these 1244 sera including repeated testing of 5 samples with initially discrepant results. Among 2820 sera from HIV-negative individuals 649 (23%) sera were WB indeterminate. The combination of Enzygnost (indirect test with synthetic peptides) and Wellcozyme (sandwich test with recombinant and synthetic peptides) Anti-HIV 1+2 EIAs was 100% specific when used for analysis of 9111 sera. One of 30,323 HIV-1 antibody negative sera tested was initially reactive on both Enzygnost Anti-HIV 1+2 and Wellcozyme Recombinant Anti-HIV-1 EIA (competitive assay) but was found to be negative by repeated testing, resulting in a specificity of 100% for that combination of ELISAs. Abbott Recombinant Anti-HIV-1 EIA (indirect assay) combined with Wellcozyme Recombinant Anti-HIV-1 EIA was initially falsely reactive with 12 of 8272 sera of which 6 were repeatedly reactive.
Conclusions: This large-scale evaluation demonstrates that combinations of two ELISAs based on different test principles and antigens increase the accuracy of the HIV antibody determination and could be used as an alternative or complement to WB.