Background and Objectives The red blood cell Mi III phenotype is prevalent in Asia, and its corresponding alloantibody, anti-Mi(a) , has been reported to cause haemolytic transfusion reactions and haemolytic disease of the newborn. However, a complete picture of the immunological characteristics of anti-Mi(a) is still lacking . We therefore conducted a systematic study to evaluate the potential clinical significance of this antibody.Materials and Methods From April 1999 to March 2000, we identified 60 sera containing anti-Mi(a) among pretransfusion samples at a teaching hospital in Taiwan. These antibodies were tested for immunoglobulin class, thermal range and activity in a monocyte monolayer assay.Results Thirty-four (57%) of the antibodies were immunoglobulin M ( IgM), and 15 retained their activity at 37 degreesC. Of those that were immunoglobulin G (IgG), 96% were of subclasses IgG1 and/or IgG3. Monocyte monolayer assay studies showed that 69% (18/ 26) of the IgG anti-Mi(a) sera were reactive.Conclusions Our study justifies the implementation of anti-Mi(a) screening in Taiwan
