Toxoid flocculation assay by laser light-scattering

Internationally accepted designations of antigen content for toxoid vaccines are provided by the WHO in Lf (limes flocculationis) units, based on the formation of antigen–antibody complexes. The current assay method for Lf determination involves observation of the complexes by eye, making the development of a more objective system highly desirable. Here we report a novel detection system using a laser light-scattering platelet aggregometer. The system was highly reproducible and more objective than the current method. Only three sets of duplicate data were sufficient for statistically significant determination of toxoid Lf by parabolic regression.