Study cites risks of older stored blood
Heart surgery patients who received transfusions of blood stored for more than two weeks were 64% more likely to die in the hospital than those who received fresher blood, a finding that adds to the growing concern about the safety of transfusion practices.
Several small studies have already suggested a danger in using blood that is nearing its expiration date, but a report published today is by far the largest, with more than 6,000 patients enrolled.
In response to the growing concern, some hospitals have modified their procedures for cardiac surgery -- one of the largest consumers of donor blood -- to minimize the need for transfusions.
New practices include increased use of blood scavenging during surgery, sending patients home with a lower-than-normal percentage of red cells in their blood, new drugs to prevent intra- and post-operative bleeding and, perhaps most important, reducing anemia before surgery.
Some researchers are also attempting to rejuvenate older blood by reinfusing it with nitric oxide, a crucial ingredient for delivering oxygen to tissues that has been shown to disappear during storage.
Many of the conservation techniques were originally developed because of fears about AIDS and other infectious agents in blood, but they have become doubly important now because of concerns about the blood itself, said Dr. Richard Shemin, chief of cardiothoracic surgery at UCLA’s Geffen School of Medicine.
“We now have very good data that shows being exposed to any blood does have a potential for harm,” he said.
But any regulatory changes are unlikely in the near future.
A statement Wednesday by the Food and Drug Administration noted that the new study in the New England Journal of Medicine was “narrow and non-randomized,” and that any regulatory actions would be “premature.”
And any action to reduce the shelf life of donor blood would significantly impair supplies, said Dr. Ross Heron, medical director of the American Red Cross. “I don’t know if we would be able to get enough blood donors to offset that,” he said.
More than 14 million units of blood are transfused every year in the U.S. Regulations let it be stored for as long as six weeks, which allows time to ship it across the country and provides a cushion against shortages. Most blood banks operate on a “first in, first out” basis, so that patients typically receive the oldest blood available. The median storage time of transfused blood is 15 days.
Because of worries about blood, Dr. Colleen Gorman Koch and her colleagues at the Cleveland Clinic looked at the records of 6,002 cardiac surgery patients who received transfusions from June 1998 to January 2006. About half had received blood that had been stored for 14 days or less, and the rest received blood stored for longer periods.
About 2.8% of those who received older blood died in the hospital, compared with 1.7% of those who received fresher blood. The rates of prolonged intubation for breathing problems, kidney failure and infections were also significantly higher in those who received older blood.
At one year after surgery, 11% of those receiving older blood had died, compared with 7.4% of those receiving fresher blood.
The older the blood, the higher the risk, Koch said.
“This is a very important outcome,” wrote Dr. John W. Adamson of UC San Diego in an editorial accompanying the report. “The results will arm those who believe that transfusion of older red-cell units carries risks and should be avoided.”
The findings won’t, and shouldn’t, change FDA policy because the study is retrospective, Koch said. To get around that problem, her group has begun a prospective study that will be randomized and blinded -- “the gold standard,” she said.
The study will involve a minimum of 2,000 patients, and results should be available in two to 2 1/2 years.
A variety of possible explanations for the risks of aging blood have been offered, in addition to the theory of nitric oxide loss.
The surface membranes of fresh red blood cells are very flexible, which allows them to deform to slip through the tiniest capillaries in the body. As the cells age in storage, the membrane becomes stiffer, increasing the possibility that the cells might block small conduits.
The cells also become stickier, increasing the likelihood of a clot.
“We are only now starting to realize what happens to blood when it is drawn out of a human body and sent to the blood bank for storage,” said Dr. Sunil Rao of Duke University.
--
