The use of an IgM immunosorbent agglutination assay to diagnose congenital toxoplasmosis.

An IgM immunosorbent agglutination assay (ISAGA) was compared with a standard ELISA IgM test for the diagnosis of congenital toxoplasmosis. It was more sensitive, detecting all of five mothers of infected babies whereas the IgM ELISA was positive in two of three mothers tested at delivery and neither of two mothers referred 10-12 months after delivery. Five women infected in a previous pregnancy had IgM detectable by ISAGA in a subsequent pregnancy. The assays were comparable when sera from patients with past infection were tested or following toxoplasma-associated miscarriage or abortion. Four cord sera from congenitally-infected babies were positive by the ISAGA but only three of these were positive by ELISA for IgM. The ISAGA also detected IgM in another four sera from congenitally-infected babies referred late (10-18 months old); none were IgM positive by ELISA. The increased sensitivity of the ISAGA is an improvement in the diagnosis of congenital toxoplasmosis.