Comparison of four serological methods for the detection of diphtheria anti-toxin antibody

The aim of this study was to compare four serological methods for the detec tion of Corynebacterium diphtheriae IgG anti-toxin antibodies (IgG-DTAb) in human serum. One hundred serum samples were evaluated for C. diphtheriae I gG-DTAb by four different methods: passive haemagglutination (PHA), latex a gglutination test (LA), toroid enzyme-linked immunosorbent assay (Toxoid-EL ISA), and toxin-binding inhibition enzyme-linked immunosorbent assay (ToBI- ELISA). As the external standardisation the neutralisation test for C. diph theriae toxin in Vero cells (TN Vero) was used. For internal standardisatio n of IgG-DTAb titres, the WHO standard serum of human diphtheria antitoxin was used. The study revealed a poor correlation between the reference test and the PHA (r=0.34 Pearson's correlation coefficient), an acceptable corre lation for the LA (r=0.74), a good correlation for the Toxoid-ELISA (r=0.81 ) and a very good correlation for ToBI-ELISA (r=0.93). The sensitivity meas urments of PHA, LA, Toxoid-ELISA and ToBI-ELISA tests, were 14, 100, 94, 96 % respectively and the corresponding specificity characteristics were 86, 7 6, 94, 90 respectively. Of the four evaluated methods, the ToBI-ELISA could be recommended for scientific and precise laboratory assays of diphtheria antibody levels in humans. For screening purposes the Toxoid-ELISA could be used, but the accuracy of antibody titres below 0.1 IU/ml, considered as t he limits of protection, is questionable. Both tests offer very useful alte rnatives to the in vitro diphtheria toxin neutralisation test in Vero cells . Because of their unsatisfactory correlation and sensitivity as compared t o the reference method, PHA and LA should be avoided and replaced by one of the two enzyme immunoassays. (C) 2000 Elsevier Science B.V. All rights res erved.