Direct Determination of Red Cell Bound Antibody Specificity

S ummary . A new method is described for direct determination of specificity of red cell‐bound antibodies without the need for antibody elution. This method employs Polybrene in an Auto Analyzer continuous flow system. Washed antibody‐coated cells are mixed, in different proportions, with uncoated indicator cells of known blood type. If the indicator cells possess appropriate receptor sites for the cell‐bound antibody, ‘coagglutination’ occurs between the antibody‐coated and indicator cells. In contrast, in the absence of specific receptor sites, indicator cells not only fail to coagglutinate but physically interfere with the expected agglutination of antibodycarrying cells. Quantitative data are provided which appear to be related to the amount of cell‐bound antibody. The technique has been used to identify antibodies with Rh and penicillin specificities and antibodies associated with acquired haemolytic anaemia.