Predictive value of latex agglutination test in serological screening for Toxoplasma gondii

The predictive value of commercial latex agglutination kit (Toxo-Screen DA, bioMerieux) was assessed for use as screening test for Toxoplasma IgG antibody. The sensivity and specificity were also compared with those of the reference standard Sabin-Feldman dye test. Five hundred serum samples were collected from 200 blood donors and 100 each from pregnant women, kidney recipients and HIV infected persons. Eighty (16.0%) out of 500 subjects were positive for Toxoplama IgG antibody by Toxo-Screen DA (bioMerieux) compared with 57 (11.4%) by Sabin-Feldman dye test. The sensivity and specificity of Toxo-Screen DA (bioMerieux) were 100% and 94.8 % respectively which were similar to previous reports from the area of high prevalence of Toxoplasma infection. In present study the positive predictive value of Toxo-Screen DA (bioMerieux) was only 71.3%. The latex agglutination test should be considered as a screening test for Toxoplasma antibody, especially by small laboratories in remote area due to its availability, simplicity, sensitivity and specificity. However, because of its moderate positive predictive value, the test should be used with caution in screening immunocompromised patients and pregnant women living in areas with low prevalence of Toxoplasma infection. Since the number of false seropositive cases would be relatively higher than in a highly prevalent area, confirmation by the dye test would be needed.