Evaluation of laboratory diagnosis of toxoplasmosis by means of an ELISA-triple test. Detection of class specific IgG, IgM and circulating antigen.

The combination of three parameters (IgG, IgM and circulating antigen) in a so-called 'ELISA triple test' was suggested for advantageous diagnosing of human toxoplasmosis. A qualitative assay was used with the following arbitrary assumptions: IgG antibodies reflect an infection, IgM antibodies reflect a recent (primary) infection and circulating antigens reflect an active infection. The three assays were performed simultaneously in one microtiter plate. This approach was tested with 1091 patient sera submitted for routine diagnosis. In comparison with conventional indirect immunofluorescence and complement fixation test it was observed that combinations indicating a recently acquired infection (combinations with IgM and/or circulating antigen) mainly paralleled low or negligible conventional antibody titers. No strict association was seen between particular combinations and certain clinical symptoms suggestive for toxoplasmosis. In conclusion it was stated that the triple test for support of clinical diagnosis has some advantages but that a strong need exists to be able to demonstrate exacerbation or reinfections which are generally not characterised by IgM antibody formation of free circulating antigens but may be the reason for elevated conventional antibody titers.