The Multispot rapid HIV-1/HIV-2 differentiation assay is comparable with the Western blot and an immunofluorescence assay at confirming HIV infection in a prospective study in three regions of the United States

BackgroundA new HIV diagnostic algorithm has been proposed which replaces the use of the HIV-1 Western blot and HIV-1 immunofluorescence assays (IFA) as the supplemental test with an HIV-1/HIV-2 antibody differentiation assay.ObjectivesTo compare an FDA-approved HIV-1/HIV-2 antibody differentiation test (Multispot) as a confirmatory test with the HIV-1 Western blot and IFA.Study designParticipants were screened with an HIV-1/HIV-2 combination Antigen/Antibody (Ag/Ab) screening assay. Specimens with repeatedly reactive results were tested with Multispot and either Western blot or IFA. Specimens with discordant screening and confirmatory results were resolved with HIV-1 RNA testing.ResultsIndividuals (37,876) were screened for HIV infection and 654 (1.7%) had a repeatedly reactive Ag/Ab assay result. On Multispot, 554 (84.7%) were HIV-1 reactive, 0 (0%) were HIV-2 reactive, 1 (0.2%) was reactive for both HIV-1 and HIV-2 (undifferentiated), 9 (1.4%) were HIV-1 indeterminate, and 90 (13.8%) were non-reactive. HIV-1 RNA was detected in 47/90 Multispot non-reactive (52.2%) specimens. Among specimens confirmed to have HIV infection (true positives), Multispot and Western blot detected HIV-1 antibody in a similar proportion of cases (93.7% vs. 94.4% respectively) while Multispot and IFA also detected HIV-1 antibody in a similar proportion of cases (84.5% vs. 83.4% respectively).ConclusionsIn this study, Multispot confirmed HIV infections at a similar proportion to Western blot and IFA. Multispot, Western blot, and IFA, however, did not confirm all of the reactive Ag/Ab assay results and underscores the importance of HIV NAT testing to resolve discordant screening and confirmatory results.