Standardization of the assay method for anti-A/B antibody titers and its problems

Introduction of effective treatments such as (double filtration) plasmapheresis, splenectomy, intravenous immunoglobulin and potent immunosuppressive agents including anti-CD20 monoclonal antibody, has greatly improved graft outcome in ABO-incompatible transplantation. The measurement of anti-blood group A/B antibody titers is considered to be important, because it would provide useful information on prognosis and indication of transplantation, selection of treatments and prediction of acute rejection. Isohemagglutinin assay in serial-doubling dilutions of serum sample by tube test has been basically used in most institutions. However, detailed assay procedure seemed to vary between institutions. Furthermore, the determination by visual observation might cause a problem of inter-examiner variability. The Japanese ABO-Incompatible Transplantation Committee has conducted a series of nationwide surveys to assess the current status of inter-institutional variation in measurement of anti-A/B antibody titer. In the first survey, serum samples from 6 healthy volunteers with blood groups A (n = 2), B (n = 2) and O (n = 2) were sent to 29 institutions where ABO-incompatible kidney or liver transplantation has been performed. Anti-A/B antibody titer was measured by its own protocol. Inter-institutional difference of measured values reached to 32-fold and 256-fold in IgM and IgG, respectively. As this variability was too wide for detailed analysis, the provisional standard protocol for the assay was determined according to the result of questionnaire survey. Next, 38 and 40 institutions participated in the second (in 2004) and the third survey (in 2005), respectively. Anti-A/B antibody titers of serum samples were measured by the standard procedure. Analysis of survey revealed that intra-institutional variation was reduced to below 8-fold (mostly 2- to 4-fold), although several institutions still needed some guidance. Standardization of the assay procedure and quality control survey would be necessary to improve the accuracy of measurement. Significance of measurement of anti-A/B antibody titer in ABO-incompatible transplantation should be discussed after the result of multi-center study is obtained.