Evaluation of the second generation IMx Toxo IgG antibody assay for detection of antibodies to Toxoplasma gondii in human sera

For an evaluation of the Abbott Imx Toxo IgG second generation, antibodies to Toxoplasma gondii were detected by Abbott Imx Toxo IgG and IgM, Vidas Toxo IgG and Toxo IgM (bioMerieux, France) with immunofluorescence assay verified by the dye-test for IgG, and immunosorbent agglutination assay (ISAGA) for IgM as references. The study included 507 serum samples collected over one month in two laboratories, 32 samples from HIV-infected patients, and 70 serial samples from 23 women surveyed for seroconversion or persistent IgM. After exclusion of nine equivocal results from the 507 samples, the sensitivity and specificity, respectively, were 100% (156/156) and 100% (342/342) for the Imx Toxo IgG and 98.1% (153/156) and 100% (342/342) for the Vidas Toxo IgG. Of the 32 HIV-infected patient samples, 7 gave false positive results with Imx Toxo IgG. This was because the samples had been heated. In 5 of the 70 serial samples, Imx Toxo IgG gave positive results earlier than Vidas Toxo IgG and in two cases earlier than IgM antibody assays. In this study Imx Toxo IgG second generation showed an increase in sensitivity and specificity in comparison with data reported previously for the first generation. J. Clin. Lab. Anal. 11:214–219, 1997. © 1997 Wiley-Liss, Inc.