Scientists have discovered that blood stored in a bank loses a vital gas that is important for transferring oxygen from the blood. As VOA's Jessica Berman reports, the discovery may explain why a significant number of people die after receiving blood transfusions.

Blood transfusion

For the past five years, experts have wondered why people who should survive after receiving a blood transfusion actually get very sick and sometimes even die of heart attack or stroke.

"This risk appears to be really quite high, three to four times of not getting a transfusion," explains Jonathan Stamler, a professor of medicine at Duke University in North Carolina.

Researchers tested samples of banked blood and discovered they had very low levels of nitric oxide, a gas in red blood cells that keeps blood vessels open so oxygen contained in the red cells can reach vital organs, including the heart.

In a study published in Proceedings of the National Academy of Sciences, Stamler and colleagues report nitric oxide in blood begin to break down almost immediately after the blood is banked.

Stamler says a companion study by another team of researchers at Duke found that the breakdown of nitric oxide begins within hours of blood collection.

"It's lost partly by three hours," he said. "About seventy percent of it is gone by a day. Maybe 80 percent or so by two days. And it remains very depleted thereafter. So there's almost no time that blood in a blood bank has adequate amounts of nitric oxide."

In the United States, blood is stored in a blood bank for up to 42 days.

Scientists tested their theory on dogs and found that low levels of nitric oxide impaired the flow of blood.

But Stamler says researchers corrected the situation by adding nitric oxide to the stored blood.

"We not only replenished the nitric oxide but restored the ability of red blood cells to dilate blood vessels. And that blood when infused into animals does a very fine job of improving blood flow and getting oxygen to tissues," he said.

Stamler says people who have lost a lot of blood and are in dire need of a transfusion should not hesitate to have one.

But he says more studies are needed to find out who would benefit most from banked blood.