Detection of immunoglobulin G antibodies to Toxoplasma gondii: Evaluation of two commercial immunoassay systems.

Background: Toxoplasmosis is a disease, which can cause severe congenital infection and is normally diagnosed by the detection of Toxoplasma gondii (T gondii)-specific antibodies in the serum of infected patients. Several different tests allow to distinguish recent from past infections and to quantify anti-T gondii-specific IgG, and the results can be used as markers for a chronic or recently seroconverted toxoplasma.

Methods: In the present study, the recent Cobas 6000 Toxo IgG assay (Roche Diagnostics, Indianapolis, IN, USA) for the serological diagnosis of toxoplasmosis was compared with the Axsym Toxo IgG assay (Abbott Laboratories, Diagnostics Division, Abbott Park, IL, USA) employing a panel of negative, low- or high-reactive serum samples that were selected after routine screening in a laboratory of clinical analyses.

Results: The overall agreement between two methods was 99% (r=0.99, p<0.001). Of 91 analyzed samples, only one presented discrepant result, being positive in the Cobas 6000 Toxo IgG assay and negative in the Axsym Toxo IgG assay. By using an immunofluorescent assay as a confirmation test, this positive result was assayed to be negative.

Conclusions: Both assays performed in each analyzer were proven to be fast and fully automated procedures for reproducible measurement of IgG antibodies to T gondii. The new method, used for the determination of anti-T gondii IgG antibodies, should be evaluated with a further analysis with increased number of serum samples to get a broad performance of this newer test.