Additional red blood cell alloantibodies after blood transfusions in a nonhematologic alloimmunized patient cohort: is it time to take precautionary measures?

BACKGROUND: Red blood cell (RBC) alloimmunization is common in transfused patients. Most studies report on the rate of alloimmunization in chronically transfused patients, which can be as high as 60 percent. Less is known on the incidence of clinically relevant antibodies in accidentally transfused patients. Because the probability of repeat transfusion increases with longer life expectancy, it was wondered to which extend non-chronically transfused alloimmunized patients are prone to form additional antibodies after repeat transfusion events. STUDY DESIGN AND METHODS: A 20-year retrospective multicenter study was performed analyzing additional alloantibody formation, against the RH, KEL, FY, JK, and MNS blood group systems. RESULTS: After additional transfusions, 21.4 percent of 653 patients produced additional antibodies, resulting in 157 new antibody specificities. At the end of the study 33.4 percent of patients had multiple antibodies. Eighty of 140 patients (57%) who formed additional antibodies did so after one transfusion episode of a median of 2 units of RBCs. Based on the antigen profile of 316 patients, 83 percent of antibodies could have been prevented by extended matching for the C, E, c, K, Fy(a), and Jk(a) antigens. Considering the current available donors in our region, 1 to 10 percent of potential donors would be available for 39 percent of patients and greater than 10 percent of potential donors for 61 percent of patients. CONCLUSION: It has been shown that nonhematooncologic alloimmunized patients are high antibody responders, with a more than 20 times increased risk to form antibodies compared to first-time alloimmunization risk. If extended matching for C, c, E, K, Fy(a), and Jk(a) antigens in the future is considered, this group should be taken into account.