For years, the medical community has known that donated blood is not as effective as it should be-a mystery that two Duke medical researchers may have solved at last.
The problem arises from the dissipation of nitric oxide, a gas responsible for keeping blood vessels open for oxygen-laden red blood cells, said Dr. Jonathan Stamler, professor of pulmonary medicine. His findings appeared in the Proceedings of the National Academy of Sciences journal this week, along with a related study by Dr. Timothy McMahon, associate professor of medicine who also studied nitric oxide's disappearance in donated blood.
"The assumption is that transfusions improve oxygen delivery to patients and thus outcomes," Stamler said. "But there's been a worrisome association between transfusion and an increased incidence of heart attacks, organ damage and even death."
Each year, 14 million transfusions are given to five million patients nationwide. Over the past decade, the use of donated blood in transfusions has dwindled as a result of these adverse consequences-to the point that many patients only receive blood after half of their own has been lost, Stamler said.
"It is important to point out that patients who are bleeding profusely do need blood, only we really don't know when to transfuse and how much," he added.
In McMahon's study, blood stored in accordance with American Red Cross standards was analyzed for nitric oxide content. Within a day, 70 to 80 percent of the gas had vanished, rendering the blood incapable of dilating blood vessels. In a transfusion, this would lead to red blood cells, carriers of life-giving oxygen, being impeded by the constricted vessels and left unable to deliver their cargo to the body's tissues. As a result, patients who do not receive this deficient blood often fare better than those who do, according to the two studies.
Stamler's study involved small transfusions into dogs, whose circulatory systems approximate those of humans. In addition to discovering the link between nitric oxide depletion and transfusion failure, the researchers may have found a simple solution-repleting stored blood with nitric oxide improved blood flow to the heart when given to animals.
"This is the first suggested solution that makes good sense," Stamler said. "Not only that, but when we put [the gas] back, in the lab, we get a restorative function too. That would be suggestive that this is at least a viable mechanism."
Both researchers suggested that this solution could be efficiently implemented in blood banks in coming years.
"I think it will stimulate a lot of interest and activity," McMahon said. "It's such a simple process that it's beautiful."
In the future, blood donations could be used therapeutically rather than as a last resort, Stamler said.
They noted, though, that more studies are needed to establish the link as conclusive.
"We need to run clinical trials now on blood transfusions-parallel studies with repleted blood to see if it can actually make people better," Stamler said.
McMahon said studies performed on patients rather than animals are still one or two years away under optimal conditions. Awareness of the detrimental effects of donated blood is low, he said, adding that the studies were rejected by several journals prior to publication in the PNAS.
"People were resistant to this idea. It makes a lot of people uncomfortable in the blood banking community," McMahon said. "Some physicians are not even fully aware of the problems."
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