Age of Packed Red Cells

Storage lesion in stored red cells is well documented, but the mechanisms involved in these changes and their affect on clinical outcomes is not well understood. The authors of an article in the November 2006 edition of Transfusion performed an exhaustive literature review related to the biochemical and biomechanical changes that occur in red cells during storage as well as summarizing observational studies of patient outcomes after red cell transfusion. An increasing amount of data suggests an association between red cell transfusion and increased morbidity and mortality that may increase with the age (i.e. collection date) of transfused red cells.

The mechanisms related to increased morbidity and mortality are still unknown, however what is known is that prolonged storage of red cells decreases their effectiveness in oxygen transport. Oxygen delivery to tissue is based on several factors: amount of hemoglobin, association and disassociation of oxygen from hemoglobin and the ability of the red cell to deform itself in order to navigate into capillaries less than half the red cell diameter. Modifications in the red blood cell during storage may also result in harm to vulnerable patients due to an inflammatory effect and toxic byproducts of storage.

Anticoagulants for red cells were developed and approved on the basis of viability and biochemical characteristics of the stored cells. Efficacy of transfusion is typically measured by change in hemoglobin levels. These measures of effectiveness have little to do with red blood cells' actual function - transport of oxygen. Few clinical trials have been developed to measure the function of tissue oxygenation.

Twenty-two observational studies involving more than 44,000 patients were reviewed. All but one study associated red blood cell transfusion with increased mortality and morbidity in critically ill patients. Another nine observational studies with more than 2,800 patients showed an association of prolonged red blood cell storage with increased morbidity and mortality. To date, only two small clinical trials assessing the clinical consequences of prolonged storage on patient outcomes have been published. Additional studies are required and the authors recommend criteria for such future studies.

Bonfils will continue to monitor these studies and inform our partners of significant findings that could affect the well-being of patients in need of transfusions.

Citation: Clinical consequences of red cell storage in the critically ill, A. Tinmouth et al, TRANSFUSION 2006; 46:2014-2027

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