Application of flow cytometry to monitor antibody levels in ABO incompatible kidney transplantation

Current methods of measuring ABO antibody levels based on the hemagglutination (HA) titers have the disadvantages of relatively poor reproducibility and do not offer fine discrimination of antibody concentration. We therefore developed a simple and rapid method of measuring ABO antibody levels using flow cytometry (FC). For validation, we analyzed plasma samples from 79 blood donors. Both IgM and IgG were detected and measured with IgG essentially restricted blood group O donors. Forty-two successive samples were collected from a patient with blood group O undergoing antibody removal and subsequent transplantation from a group A2 donor and tested by both HA and FC. Changes in IgG measured by FC (relative median fluorescence) correlated well with HA titers and importantly rejection episodes were preempted by a rising relative median fluorescence. The method allowed quantitative discrimination in the range of antibody levels relevant to ABO incompatible transplantation and has the advantages over HA of objective measurement and reproducibility.