Comparative performance of ISAGA IgM and ELISA assays for the diagnosis of maternal and congenital Toxoplasma infections: which technique could replace ISAGA IgM?

The ISAGA immunocapture test for the detection of anti-Toxoplasma immunoglobulin M is a manual technique known for its excellent sensitivity and specificity. The purpose of this retrospective, multicenter study was to compare the performances and agreement between ISAGA and other IgM detection techniques before cessation of ISAGA production. The analytic performance of the different tests was evaluated using 1,341 serum samples from adults with positive IgM and negative IgG to Toxoplasma gondii, and 1,206 sera from neonates born to mothers with seroconversion. The agreement between the tests was evaluated on 13,506 adult and 5,795 child serum samples. The sensitivity of Toxo-ISAGA IgM (adults 98.7%, neonates 63.1%) was similar to that of Platelia Toxo IgM (adults 94.4%, neonates 64.6%), and significantly higher than Liaison Toxo IgM (adults 90.6%), Architect/Alinity Toxo IgM (adults 95.7%, neonates 48.6%), and Vidas Toxo IgM (adults 81.8%, neonates 17.5%). However, the specificities varied between 24.4% (Platelia Toxo IgM) and 95.2% (Liaison Toxo IgM) in adults and were >95% for all tests in neonates. An analysis of the kappa coefficients showed better agreement between ISAGA IgM and the other tests in children (0.75-0.83%) than in adults (0.11-0.53%). We conclude that, in the absence of Toxo-ISAGA IgM, the association of a very sensitive technique (Platelia Toxo IgM or Architect/Alinity Toxo IgM) and a very specific technique (Vidas Toxo IgM or Liaison Toxo IgM) is recommended for IgM detection in adult sera. For neonates, Platelia Toxo IgM appeared to be the best alternative to replace Toxo-ISAGA IgM.