Comparison of four different immunoassays for detection of Toxoplasma-specific immunoglobulin G

Serum specimens from 246 women of childbearing age were tested for immunoglobulin G (IgG) antibodies to Toxoplasma gondii by four different commercial assays: Abbott IMx microparticle enzyme immunoassay (EIA), Mercia Toxo-G EIA, Bartels Prima EIA, and bioMerieux Vitek (VIDAS) enzyme-linked fluorescent assay. A total of 27 specimens were initially positive with all four assays, 202 specimens were negative, and 17 specimens were discrepant (disagreement among the assays). After repeating tests for the 17 discrepant samples, five resolved (one was positive and four were negative). The 12 remaining discrepant samples were tested by an indirect fluorescent antibody (IFA) assay for Toxoplasma IgG antibodies; five specimens were positive for Toxoplasma IgG by IFA. The resolved sensitivities of the various kits ranged from 88% (bioMerieux VIDAS) to 94% (Abbott IMx), and the specificities were all 98%-99%. These results show that the four serologic tests used for detection of Toxoplasma IgG give very similar results and can all be readily used by clinical laboratories for screening purposes.