[IgM ISAGA test in the diagnosis of acute acquired Toxoplasma infections]

An immunoglobulin M immunosorbent agglutination assay (IgM ISAGA) was tested in 1804 outpatients' samples. The test was negative in all 1091 sera from individual negative in the total indirect immunofluorescence antibody (IFA tot) test and in the passive hemagglutination (HA) test and in 15 sera with inconclusive results in these two tests. The 698 sera positive in the IFA tot and HA tests were also tested with direct IgM enzyme-linked immunosorbent assay (IgM ELISA). The 74 sera positive in the IgM ISAGA and/or IgM ELISA were also tested in the IgM immunofluorescent (IgM IFA) test. These sera belong to 42 individuals, 26 of whom were followed for previous positive results in the IgM ELISA test. 51 samples (68.9%) were found positive in both IgM ISAGA and IgM ELISA tests. Only 13 (25.5%) of these 51 samples were found positive in the IgM IFA. 9 samples (12.2%) were positive only in the IgM ISAGA test. Conversely another 9 samples (12.2%) were positive only in the IgM ELISA test, performed on serum as well as on chromatographic IgM fraction. Finally five samples (6.7%) yielded false positive results in the IgM ELISA test, and three of them were found false positive also in the IgM IFA test. All these five samples in fact were found negative on IgM chromatographic fraction in both tests. In conclusion, IgM ISAGA appears to be more specific than direct IgM ELISA or IgM IFA test for the detection of Toxoplasma gondii IgM. Sensitivity of IgM ISAGA test seems to be as good as in the direct IgM ELISA and better than in the IgM IFA test for the diagnosis of acute acquired toxoplasma infection.