Anti-diphtheria toxoid antibodies are raised in response to vaccination with diphtheria toxoid protein. A patient's response to the immunisation may be assessed, subsequently, by the serological determination of the anti-diphtheria toxoid antibody level using this quantitative enzyme immunoassay technique. It should be noted that the reference method, particularly in Europe, may be the Vero Cell Assay (VCA). This assay gives a measurement of the amount of `neutralising' antibody of all immunoglobulin classes, not only IgG. Historically, comparison of commercial ELISA kits and the Vero Cell Assay has shown poor correlation, as the ELISA may detect a proportion of specific antibodies that may not neutralisethe diphtheria toxoid. As the assay utilizes the diphtheria vaccine for coating the plate, the assay gives a measurement of specific IgG antibodies produced in response to vaccination. Intended Use: BioAssay? Kit is intended for the in-vitro measurement of specific IgG antibodies