Clinical studies of the effect of blood storage on patient outcomes.

It is indisputable that there are numerous biochemical, structural, inflammatory, and physiologic changes in stored red cells, sometimes referred to collectively as the "red cell storage lesion". It remains controversial however whether any of these changes have clinical relevance and actually impact the clinical outcomes in transfused patients. More than 25 published clinical studies have evaluated the effects of red blood cell storage on patient outcomes. The majority of studies are non-randomized observational studies with methodologic limitations described in this review. These studies do however provide equipoise to support the ethical conduct of the large, definitive randomized clinical trials which are now underway.