Transfusion of older red blood cell units, cytokine burst and alloimmunization: a case-control study.

BACKGROUND Experimental data have shown that the transfusion of older red blood cell units causes alloimmunization, but the clinical applicability of this statement has never been properly assessed in non-sickle cell patients. It has been hypothesized that older units have higher numbers of cytokines, increasing the risk of alloimmunization related to antigen-presenting events. The goal of this study was to evaluate the association between the transfusion of older red blood cell units subjected to bedside leukodepletion and alloimmunization. METHODS All patients submitted to transfusions of bedside leukodepletion red blood cell units proven to have become alloimmunized in one oncologic service between 2009 and 2013 were enrolled in this study. A control group was formed by matching patients without alloimmunization in terms of number of transfusions and medical specialty. The median age of transfused units, the percentage of transfused red blood cell units >14 days of storage in relation to fresher red cell units (≤14 days of storage) and the mean age of transfused units older than 14 days were compared between the groups. RESULTS Alloimmunized and control groups were homogeneous regarding the most relevant clinical variables (age, gender, type of oncological disease) and inflammatory background (C-reactive protein and Karnofsky scale). The median age of transfused red blood cell units, the ratio of older units transfused compared to fresher units and the mean age of transfused units older than 14 days did not differ between alloimmunized and control patients (17 vs. 17; 68/32 vs. 63.2/36.8 and 21.8±7.0 vs. 21.04±7.9; respectively). CONCLUSION The transfusion of older red blood cell units subjected to bedside leukodepletion is not a key risk factor for alloimmunization. Strategies of providing fresh red cell units aiming to avoid alloimmunization are thus not justified.