Total plasma heme concentration increases after red blood cell transfusion and predicts mortality in critically ill medical patients

BACKGROUND Relationships between red blood cell (RBC) transfusion, circulating cell‐free heme, and clinical outcomes in critically ill transfusion recipients are incompletely understood. The goal of this study was to determine whether total plasma heme increases after RBC transfusion and predicts mortality in critically ill patients. STUDY DESIGN AND METHODS This was a prospective cohort study of 111 consecutive medical intensive care patients requiring RBC transfusion. Cell‐free heme was measured in RBC units before transfusion and in the patients' plasma before and after transfusion. RESULTS Total plasma heme levels increased in response to transfusion, from a median (interquartile range [IQR]) of 35 (26–76) μmol/L to 47 (35–73) μmol/L (p