Washington: A new study of hospital patients has found that transfusion of donated blood more than three weeks old results in impaired blood vessel function.Blood banks now consider six weeks to be the maximum permitted storage time of blood for use in transfusion, but recent studies have suggested transfusing blood stored for more than a few weeks has adverse effects in patients undergoing cardiac surgery or critical care.The new finding has suggested a mechanism explaining why older blood might be detrimental to patient health: a deficiency in nitric oxide, a short-lived chemical messenger that relaxes blood vessels.Cardiovascular research fellow Robert Neuman, MD presented the results at the American College of Cardiology meeting in San Francisco. Senior authors include Arshed Quyyumi, MD, professor of medicine and director of the Emory Clinical Cardiovascular Research Institute, and John Roback, MD, PhD, associate professor of pathology and laboratory medicine and medical director of the Emory University Hospital blood bank.In the current study, 43 patients at Emory University Hospital were set to receive cross-matched red blood cells for clinical indications. Members of the group were in hospital for various reasons, such as cancer treatment and surgery. They were randomly chosen to receive either fresh (less than ten days old) or aged (more than three weeks old) red blood cells. On average, they received the equivalent of two units. A unit is 450 milliliters of blood.Neuman and his colleagues tested blood vessel function by measuring flow-mediated dilation (FMD). By ultrasound, they tested how much a blood vessel in the arm opens up after a blood pressure cuff is first tightened then removed. Flow-mediated dilation is an indicator of the health of the endothelial lining of the blood vessels and is a process that is dependent on nitric oxide.Healthy, younger individuals can have flow-mediated dilation of up to 10 percent - the average for the hospitalized group was 5 percent. Patients receiving aged blood saw their FMD halved to 2.4 percent 24 hours after the transfusion, while patients receiving fresh blood saw no significant change in FMD.
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