Red cells in blood stored longer than three weeks gradually lose the flexibility required to squeeze through the body's smallest capillaries to deliver oxygen to tissue, a new study has claimed.
Moreover, that capacity is not regained after transfusion into patients during or after surgery, researchers from Johns Hopkins University found.
"There's more and more information telling us that the shelf life of blood may not be six weeks, which is what the blood banks consider standard," said study leader Steven M Frank, an associate professor of anesthesiology and critical care medicine at the Johns Hopkins University School of Medicine.
Frank said the current practice of transfusing blood stored up to six weeks may need to be reconsidered.
Frank and his colleagues enrolled 16 patients scheduled to have spinal fusion surgery, a type of operation that typically requires blood transfusions.
Six of the patients received five or more units of blood, while 10 needed three or fewer units. The researchers drew samples from every bag of blood used � 53 in total � and measured the flexibility of the red blood cells.
They found that blood older than three weeks was more likely to have less flexible red blood cell membranes, a condition that may make it more difficult for blood to deliver oxygen, Frank said in a statement.
The team also took blood samples from patients in the three days following surgery. Even though the blood cells were out of storage and back in biological environments with proper pH (acidity), electrolytes and oxygen levels, the injury to the red cells was not reversible and appeared to be permanent.
The damaged blood cells would likely remain dysfunctional for their life cycle limit, which is up to 120 days, Frank said.
Frank also noted that patients in the study who got fewer units of blood had healthier red cells overall, even though the blood was just as old and showed cell damage.
He said it is likely that a small amount of these problem cells make less of a difference than when a large number of damaged cells are present.
According to the research report, the average age of the blood given in the study was more than three weeks. Only three samples in the study were two weeks old or less.
Two large randomised controlled studies, one at many centres across the United States, including Johns Hopkins, and one in Canada, are under way to determine the relative safety of older versus newer blood, and the results are expected next year.
The study was published in the journal Anesthesia & Analgesia.
