A novel IgM-indirect hemagglutination test for the serodiagnosis of acute toxoplasmosis.

A new indirect hemagglutination (M-Toxo-IHA) test was standardized for the serodiagnosis of acute toxoplasmosis. The reagent for this test consisted of stabilized human red cells coated with a Toxoplasma gondii heat-stable alkaline-solubilized extract which reacted predominantly with IgM antibodies found in serum samples from patients with a recent infection. Almost no reactivity was verified with serum samples from chronic or ancient toxoplasmosis. The reagent preparation was simple and obviated prior fractionation of parasite components reactive with IgM antibodies. Rheumatoid factor or high levels of IgG antibodies did not interfere in the M-Toxo-IHA test. A total of 358 serum samples was assessed for the evaluation of this test, comprising sera from patients with recent and ancient toxoplasmosis, from non-related diseases, as well as from clinically healthy individuals with no previous T. gondii infections. Serodiagnostic performance of the M-Toxo-IHA test in terms of sensitivity, specificity, efficiency, and positive and negative predictive values was verified, and the values obtained were 1.000, 0.985, 0.989, 0.952, and 1.000, respectively, in relation to IgM-immunofluorescence or IgM-capture ELISA. Six different batches of reagent, successively produced for the current study, provided reproducible results and were stable for at least 22 months at 4 degrees C.