Shelf life of blood? Shorter than we think

A small study from Johns Hopkins adds to a growing body of evidence that red blood cells stored longer than three weeks begin to lose the capacity to deliver oxygen-rich cells where they may be most needed.

In a report published online in the journal Anesthesia & Analgesia, investigators say red cells in blood stored beyond three weeks gradually lose the flexibility required to squeeze through the body's smallest capillaries to deliver oxygen to tissue. Moreover, they say, that capacity is not regained after transfusion into patients during or after surgery.

"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," says study leader Steven M. Frank, an associate professor of anesthesiology and critical care medicine at the Johns Hopkins University School of Medicine. "If I were having surgery tomorrow, I'd want the freshest blood they could find."

Frank acknowledges that blood banks do not have enough fresh blood for everybody, and that shorter storage periods would result in diminished inventory. But he says that the current practice of transfusing blood stored up to six weeks may need to be reconsidered.

One previous, large study published in the New England Journal of Medicine showed that cardiac surgery patients who received blood stored longer than three weeks were almost twice as likely to die as patients who got blood that had been stored for just 10 days.

For the new study, 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 says.