Concordance between ELISA and IFA, for IgG antibodies detection against Toxoplasma gondii

Objective. To measure the degree of correlation between the indirect fluorescence antibody test (IFAT) and the ELISA techniques used for the detection of anti-Toxoplasma gondii IgG antibodies in humans. Materials and methods. We conducted a comparative study of two diagnostic techniques for the detection of anti-T. gondii IgG, using 243 human serum samples, collected during the years 2000-2006, from the serum collection of the Laboratorio de Parasitología- Red Nacional de Laboratorios of the Instituto Nacional de Salud. Results. The percentage of reactivity for anti-T.gondii IgG was 54% (131 sera) by the IFAT technique and 56.3% (137 sera) by the ELISA technique, while 46% (112 sera) of the samples were negative by IFAT and 44% (106 sera) by ELISA. The kappa value was 0.916 (95%CI: 0.866 – 0.976), which reflects an almost perfect agreement between the two techniques. Conclusions. The kappa index shows an almost perfect agreement between ELISA and IFAT. This will help the departmental public health laboratories of the country to comply with the determination of IgG anti-T.gondii as a diagnostic tool during prenatal care, if they do not have the infrastructure needed for the IFAT, bearing in mind that ELISA is based on the degree of affinity of antibodies for a specific antigen and does not measure the actual antibody level in a serum sample, as does the IFAT technique.