Performance characteristics of a commercial antibody-capture enzyme immunoassay for detection of Toxoplasma-specific IgM antibodies.

Antibody-capture enzyme immunoassay (EIA) for the detection of Toxoplasma-specific IgM has been shown to provide significantly higher specificity than the indirect IgM EIA. A new commercially available antibody-capture EIA (PLATELIA Toxo IgM EIA) converted 99 out of 100 false-positive Toxo-plasma IgM determinations to true negative. Experiments using Toxoplasma IgM calibrators demonstrated the antibody-capture EIA is approximately eightfold more sensitive than a new automated microparticle EIA for Toxoplasma IgM antibodies (IMX Toxo IgM EIA), and approximately equal in sensitivity to the indirect immunofluorescence assay. Precision studies of the antibody capture EIA using low, medium, and high calibrators gave coefficients of variation ranging from 3.0%-4.5% for within-run and 5.2%-11.4% for run-to-run variation experiments. Interference from high levels of bilirubin, albumin, hemoglobin, and lipid was not detected. Sera from patients with inflammatory or infectious disorders were tested for interference in the antibody-capture EIA. False-positive Toxoplasma IgM results were not observed, but low-level negative interference was detectable when patient sera was mixed with Toxoplasma-positive sera. Preparations of purified human IgM also produced negative interference in the antibody-capture EIA for Toxoplasma IgM.