The temporal distribution of red blood cell transfusions is associated with alloimmunization risk

Abstract Background Red blood cell (RBC) transfusion causes RBC alloimmunization in a st of patients. Factors that influence RBC alloimmunization risk are incompletely understood. Study Design and Methods We performed a matched case–control study of male intensive care unit (ICU) patients who did or did not develop a new RBC alloantibody after RBC transfusion. Demographic, clinical, and laboratory data were collected. Cases and controls were matched 1:2 on serological follow‐up time (SFT) and the number of RBC units transfused. Conditional logistic regression analyses were performed to identify variables associated with the development of a new RBC alloantibody. Results One hundred and seventeen cases who developed a new RBC alloantibody during the SFT were matched with 234 controls who did not develop an alloantibody. The median SFT was 40 days among cases and 52 days among controls. The median number of RBC units transfused during the SFT was 7 in both groups. Although the total number of RBC units transfused was similar, cases were transfused RBC units in fewer transfusion episodes compared with controls. The median number of transfusion episodes, defined as a minimum time interval of 24 h between RBC transfusions, was higher in controls compared to cases. In multivariable analysis, each additional transfusion episode was associated with a 26% lower risk of RBC alloimmunization (odds ratio 0.74; 95% confidence interval 0.63–0.86; p < 0.001). Conclusions In a matched case–control study of male ICU patients who received a similar number of RBC transfusions, a greater number of transfusion episodes was associated with a decreased risk of developing a new RBC alloantibody.