Strategies for detecting toxoplasma immunity.

A strategy for identifying toxoplasma immunity in pregnancy must provide good evidence of immunity but not falsely reassure; that for immunocompromised patients should identify immunity and also the risk of reactivated toxoplasmosis. Using sera from both of these patient groups, the performance of an in-house IgG EIA and two commonly used commercial assays (Abbott AxSYM Toxo-G and Eiken latex test) were compared with the dye test. False-positive results were obtained using the IgG enzyme immunoassay (EIA) and AxSYM Toxo-G, and false negatives using all three screen tests. During pregnancy, positive results may falsely reassure, and patients should be tested for toxoplasma-specific IgM to differentiate between current infection and immunity. In immunocompromised patients, positive results indicate immunity but negative results do not exclude it; these should be tested by dye test. Despite these reservations, we have demonstrated that immunity screening can be performed within a district general hospital.