Red‐blood‐cell alloimmunization and prophylactic antigen matching for transfusion in patients with warm autoantibodies

Background Warm autoantibodies (WAA) are antibodies that react with an antigen on a patient’s own red‐blood‐cells and can complicate compatibility testing whether or not they cause clinical haemolysis. The goal of this study was to understand the overall prevalence of WAA, the risk of RBC alloimmunization and determine whether RBC selection practices have an impact on alloimmunization. Materials and methods Records of patients (>1 year of age) with an indirect antibody detection test (IAT) and serologic evidence of WAA over a 10‐year‐period were included. Eight centres from 5 countries collectively reviewed 1 122 245 patients who had an IAT. Results Of patients having IAT, 1214 had WAA (0·17%). Transfusion information for 1002 of the patients was available; 631 were transfused after identification of the WAA (63%); of the transfused patients, 390 received prophylactic antigen‐matched (PAM) RBCs and 241 did not. Of the 372 patients with WAA who were transfused and had serologic testing 30+ days following transfusion (30–2765 days), 56 developed new RBC alloimmunization (15·1%). Patients who were transfused using a PAM strategy were not protected from new RBC alloimmunization [14·6% (31 of 212 patients) having PAM transfusion approach compared with those not receiving PAM approach (15·6%, 25 of 160 patients, P = 0·8837)]. Conclusions The prevalence of WAA in patients having an IAT is low (