<<Print>>

Using donated blood that is more than three weeks old for transfusions could harm health as much as eating fatty foods or smoking, new research suggests. Blood banks consider six weeks to be the maximum storage time for blood used in transfusions. But a new study suggests that transfusing blood stored for more than a few weeks could negatively affect how patients' blood vessels work. Experts believe the reason for this is because older blood has less nitric oxide, a chemical messenger that relaxes blood vessels. Over time in storage, nitric oxide in the blood is lost. Nitric oxide signals the blood vessels to dilate, or expand, and is also involved in transporting oxygen to the tissues. Just last week, researchers at Johns Hopkins University in Baltimore reported that blood older than three weeks may suffer irreversible damage and not be as effective. After just three weeks on the shelf, blood cells become more rigid, making it difficult for them to penetrate smaller capillaries, says the study published in the journal of the International Anesthesia Research Society. A 2008 study published in the New England Journal of Medicine found that cardiac surgery patients receiving older blood had a higher risk of dying in the hospital, and were more likely to need ventilation support or have sepsis or kidney failure. Two large-scale clinical trials are currently addressing the issue of the maximum time blood should be stored. The new study, to be presented at the American College of Cardiology meeting in San Francisco, looked at patients who were randomly chosen to receive either fresh (less than ten days old) or aged (more than three weeks old) red blood cells. Experts used ultrasound to test blood vessel function by measuring flow-mediated dilation (FMD) - a process dependent on nitric oxide. Measuring it involved seeing how much a blood vessel in the arm opened up after a blood pressure cuff was first tightened then removed. FMD is an indicator of the health of the endothelial lining of the blood vessels (and the state of the lining can indicate a person's risk of heart disease). Healthy, younger individuals can have FMD of up to 10 per cent. The average for the participants was five per cent. Patients receiving aged blood saw their FMD halved to 2.4 per cent 24 hours after the transfusion. But patients receiving fresh blood saw no significant change in FMD. This effect of older blood on blood vessel function is similar to that of eating a fatty meal or the long term effects of a heart disease risk factor, such as smoking or diabetes, the researchers said. Although blood banks tend to use a 'first-in, first-out' policy, limiting storage time could reduce the blood supply, they warn. One possibility could be to reserve fresh blood for those patients at most risk of cardiovascular problems, said lead study author Professor Robert Neuman, cardiovascular research fellow at Emory University. Another way that nitric oxide deficiency could be remedied is with an additive such as nitrite, which the body uses as a storage reservoir for nitric oxide, or some other preservative. Professor Neuman added: 'There is a lot of information that blood that has been stored for a while can cause problems for patients. 'This starts to answer the question: what is causing the problem?'