Most incidentally transfused patients receive only ABO-D–compatible transfusions and antibodies are formed in up to 8%. The effect of extended (c, C, E, K, Fya, Jka, and S antigens) matched (EM) and ABO-D–matched red blood cell (RBC) transfusions on the incidence of new clinically relevant RBC antibody formation after a first elective transfusion event in surgical patients was studied.STUDY DESIGN AND METHODS:
A multicenter randomized trial was performed in nontransfused patients who were scheduled to experience a single elective transfusion event of maximal 4 RBC units. The primary outcome was the incidence of newly formed warm reacting clinically relevant RBC alloantibodies measured in three follow-up (FU) samples taken at 7 to 10 days, 4 to 6 weeks, and 4 to 6 months posttransfusion.RESULTS:
A total of 853 patients were randomized, and of these, 333 patients were transfused with a total of 1035 RBC units. At least one FU sample was available from 97% of transfused patients. In intention-to-treat analysis, new antibodies were detected in 10 of 155 ABO-D and seven of 178 EM patients, respectively. Per-protocol analysis including 190 patients showed a nonsignificant absolute risk difference (ARD) of 5.3% (95% confidence interval [CI], −1.4% to 12%) in alloimmunization between study arms. In a post hoc analysis of 138 patients who received RBCs but no platelet (PLT) transfusions the ARD increased to significance, 8.0% (95% CI, 0.4-16.0).CONCLUSION:
Extended matching for selected antigens reduced the alloimmunization risk by 64% in surgical patients. Extended matching seems successful only if the patient did not receive accompanying nonmatched PLT transfusions.