03/06/2013 10:26 am ET

Blood Shelf Life May Be Shorter Than Previously Thought

Donated blood may not last as long in storage as previously thought, according to a small new study in the journal Anesthesia & Analgesia.

Right now, the Food and Drug Administration permits red blood cells to be stored for as long as six weeks (42 days). However, according to the new study, researchers found that red blood cells stored any longer than three weeks lose the flexibility they need to get through tiny capillaries throughout the body. And if they can't travel through the capillaries, then the red blood cells aren't able to bring oxygen to needed places in the body.

"If I were having surgery tomorrow, I'd want the freshest blood they could find," study researcher Dr. Steven M. Frank, M.D., who is an associate professor of anesthesiology and critical care medicine at the Johns Hopkins School of Medicine, said in a statement. Frank has consulted for blood storage companies before, but the university noted that the companies don't benefit from the new findings.

The study included 16 people who were going to undergo spinal fusion surgery, and needed blood transfusions. Some of the participants needed more blood than others; in total, 53 bags of blood were used. The average age of the blood was more than three weeks old, and only two of the samples gathered in the study were obtained fewer than two weeks prior.

Researchers analyzed the flexibility of the red blood cell membranes of the transfused blood, and found that the blood that was more than three weeks old had worse flexibility than newer blood.

Then, after all the participants had undergone their necessary surgeries, researchers took blood samples from them to see if the flexibility had improved at all since being in the body. However, they found that the red blood cells were still damaged, even though they were back in the body.

The study follows previous research on potential harms of using older blood. A past study in the New England Journal of Medicine showed that death risk doubled for people if they got blood that had been stored for longer than two weeks during cardiac surgery, compared with those who received blood that had only been in storage for 10 days.