Comparison of the Toxin Binding Inhibition assay (ToBI) with the Double Antigen ELISA (DAE) for the determination of antibody titers against diphteria toxin in human serum
Vergelijking van de Toxine Bindings Inhibitie test (ToBI) met de Dubbel Antigeen ELISA (DAE) voor het bepalen van antistoftiters tegen difterie toxine in humaan serum
Knipping CT, Berbers GAM
RIVM Report 126000001
Both assays can possibly substitute the Vero Neutralisation assay (NT). Because the NT is not suited for the determination of large numbers of serum samples, the ToBI was developed in the late eighties within the RIVM and has been internationally accepted. Recently, the DAE has been developed in Copenhagen and published as possible alternative for the NT. When the ToBI and the DAE are performed with a twofold serial dilution of the serum samples both assays show a good correlation with the NT and with each other. The sensitivity of the DAE seems comparable with the NT, while the ToBI shows to be less sensitive (a factor 5 - 10). For both assays the criterium of protection of 0.1 IU/ml can easily be accurately measured, while the minimum immune titre of 0.01 IU/ml can also be applied. However , if in both the ToBI and the DAE in stead of serial dilution series a two- or threepoints dilution of the serum is used to increase the number of samples per plate (factor 6), the correlation decreases in such a way that the reliability of the results has become doubtful. The conclusion of this investigation is that both the ToBI and DAE performed with twofold serial dilutions are reliable alternatives of the NT. Both tests are equally well applicable with regard to the speed of assay performance and the number of serum samples to be assayed in one week. The possibility to use DAE/DELFIA (Delayed time-resolved fluorescence immuno assay) or ToBI with a single or a limited number of dilutions of the sera is not recommended, espe-cially in the lower titres where a discrimination between positive and negative sera has to be established.
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