Abstract: Objective  To develop an indirect immunofluorescence assay （IFA） kit for detecting anti-Toxoplasma gondii IgG.  Methods  Based on the established IFA method, we established an IFA kit for the detection of human T. gondii infection. The optimal working concentrations of T. gondii IgG-positive human serum and FITC-labeled goat anti-human IgG antibody were determined. Sensitivity, specificity, reproducibility, and storage period of this kit were studied, and compared with an imported kit.  Results  The optimal working concentration of T. gondii IgG-positive human serum and FITC-labeled goat anti-human IgG antibody was 1 ∶ 40 and 1 ∶ 100, respectively. The maximum dilution of T. gondii IgG-positive human serum that the kit can detect was 1 ∶ 640. No cross reaction was observed with sera from patients with vivax malaria, falciparum malaria, schistosomosis, echinococcosis, or cysticercosis. Cross reaction was observed to the rheumatoid factor positive sera. The sensitivity, specificity, positive predictive value, negative predictive value, concordance, Youden index of this kit was 90.9%, 100%, 100%, 96.2%, 97.2%, and 0.91, respectively; and that of the imported kit was 100%, 98%, 95.7%, 100%, 98.6%, and 0.98, respectively. There was no significant difference in sensitivity and specificity between the two kits (P＞0.05).  Conclusion  The IFA kit shows adequate sensitivity and specificity for detection of anti-T. gondii IgG.

Key words: Toxoplasma gondii, Toxoplasmosis, Indirect immunofluorescence assay, IgG antibody