The common practice of storing blood for more than two weeks could be proving fatal for thousands of heart surgery patients, according to a major study.
Doctors at the Cleveland Clinic in Ohio have found that patients who receive blood that is more than 14 days old are nearly two-thirds more likely to die than those who get newer blood.
The survey of more than 9000 heart surgery patients also suggests that recipients of older blood are more at risk from blood poisoning and organ failure. The conclusion? "Blood should be classified as outdated earlier than current recommendations," says lead researcher Colleen Koch. Koch's team note that in the US the average age of transfused blood is more than two weeks - and that around half of all heart surgery patients receive blood transfusions.
New measures are urgently needed, say the researchers, to prevent unnecessary deaths among this large and vulnerable group of patients. Previous studies have suggested that transfusions increase the risk of death and serious complications. This latest study suggests the age of the blood used is a major factor.
Broken blood
On the basis of earlier laboratory studies, Koch speculates that, at the two-week stage, stored red blood cells begin to break down. This, she says, may make them more likely to block blood vessels while reducing their capacity to carry oxygen. Her team studied the medical records of patients who received major heart surgery at the Cleveland Clinic between June 1998 and January 2006.
A total of 2,872 patients received blood that had been stored for 14 days or less, and 3,130 patients received blood that was more than 14 days old. The mean storage age was 11 days for the newer blood and 20 days for the older blood. In-hospital mortality was significantly higher among those who received older blood: 2.8% compared to 1.7%.
The researchers also found that death rates a year on were nearly half as high again in the patients who had received older blood, compared to those who received newer blood. 11% of the patients who had received older blood had died a year later, compared to 7.4% of those who received newer blood. Both sets of patients received the same volume of blood.
"This research suggests that the longer transfused blood has been stored, the greater the risk of complications following cardiac surgery," says Peter Weissberg of the UK charity, the British Heart Foundation. He says that research last year indicated that, in many heart surgery patients, transfusions did more harm than good.
"Together, these studies suggest that only those heart patients whose lives are at serious risk without a transfusion should receive blood," Weissberg says.
"Further research is urgently needed to clarify the indications for transfusion and the effects of blood storage on outcome."
There are around 30,000 heart operations every year in the UK, and over 100,000 in the US.
Journal refs: New England Journal of Medicine, vol 358, p1229
Circulation, vol 116, p2544
