CHICAGO - BLOOD transfusions may do more harm than good for a majority of patients because banked blood begins to lose a key gas almost immediately after it is donated, researchers said on Monday.

Nitric oxide facilitates the transfer of oxygen from red blood cells to tissues but it begins to be lost within three hours of being banked, according to two studies from Duke University Medical Centre.

'The issue of transfused blood being potentially harmful to patients is one of the biggest problems facing American medicine,' said Jonathan Stamler, a professor of cardiovascular and pulmonary medicine at Duke.

'In principle, we now have a solution to the nitric oxide problem - we can put it back - but it needs to be proven in a clinical trial.' Prof Stamler's team has already managed to increase blood flow to the hearts of oxygen-deprived dogs after they added nitric oxide back to banked blood. The next step is to see if this technique also works in humans.

Higher incidences of heart attack
A number of recent studies have found that patients who receive blood transfusions have higher incidences of heart attack, heart failure, stroke and even death. But this is the first study to identify why.

'Nitric oxide opens up the tiny blood vessels, allowing red blood cells to pass and deliver oxygen,' Prof Stamler said.

'If the blood vessels cannot open, the red blood cells back up in the vessel and tissues go without oxygen. The result can be a heart attack or even death.'

Nitric oxide might also influence the flexibility of the saucer-shaped blood cells. The studies also found that the red blood cells become stiffer as nitric oxide levels decrease, making it hard for them to squeeze through tiny blood vessels.

The studies were published in the Proceedings of the National Academy of Sciences. -- AFP