Quantitation of proteins in the femtomole range by hemagglutination using an electronic particle counter

By using an electronic particle counter equipped with two counting channels, it is possible to simultaneously count total particles and agglutinated particles in an erythrocyte population. Using these two parameters, an empirically useful measure of the degree of agglutination in a sample (the agglutination index) can be generated. This method has been used to accurately and precisely determine human serum IgG concentrations in an inhibition of hemagglutination assay. As little as 1 microgram/ml of IgG could be measured in this way. Agglutination and inhibition of agglutination assays with other systems indicate that this method will be widely applicable.