[Critical study of ELISA technique and high sensitivity direct agglutination test for the screening of antitoxoplasma IgG].

The authors have evaluated an ELISA (Toxo-IgG EIA; bioMérieux) and a direct agglutination test using a sensitized antigen (Toxo-Screen DA; bioMérieux), with a fluorescent test antibody (Toxo-Spot IF; bioMérieux) as a reference for the screening of toxoplasmosis IgG antibodies. A good correlation was obtained for these two methods with fluorescent test antibody (p less than 0.00001) on 841 sera. However, results obtained with direct agglutination test were better than those obtained with ELISA (direct agglutination versus fluorescent test antibody: 97.4% of agreement; ELISA versus fluorescent test antibody: 96.1% of agreement). In addition, the use of the Receiver Operating Characteristic (ROC) curve, showing the changes of sensitivity and specificity as a function of the possible values of each threshold, indicated that sera with titers between 15-20 IU/ml should be interpreted very cautiously.