Blood Shelf Life Shorter Than Previously Thought
Alan McStravick for redorbit.com – Your Universe Online
Over the past five years, studies have been conducted exploring the efficacy of transfused blood in delivering oxygen throughout the body. More specifically, those studies focused on the breakdown of nitric acid contained in red blood cells. The deterioration of the nitric acid begins almost immediately after blood is drawn from a donor. Regardless of how much oxygen may be contained in a red blood cell, if there is an insufficient quantity of nitric acid to open the blood vessels, that oxygen simply cannot reach the tissues.
In the March 20, 2008 edition of the journal New England Journal of Medicine, researchers looked specifically at the complications and mortality rates after a cardiac surgery where the patient received transfused red blood cells. They culled over nearly a decade’s worth of patient data, separating the patients into one of two categories, based solely on the storage age of the blood they received. Those classified in the “newer blood” grouping received blood that had been stored no more than 14 days. Those individuals in the “older blood” group had received blood stored for more than two weeks.
The results of that study found patients who received older units suffered significantly higher rates of in-hospital mortality, incubation beyond 72 hours, kidney failure and sepsis (or septicemia). The receipt of older units typically presented a composite of these complications for the patient.
On the other hand, those patients who received the newer units had a far lower mortality rate through the first year after the procedure.
The research team for the 2008 study came to the conclusion patients who undergo cardiac surgery where the transfused red cells were stored for more than two weeks were more likely to experience risk associated with postoperative complications as well as reduced short- and long-term survival.
In a more recent study out of Johns Hopkins, a research team has built upon previous research and found the blood bank system in the US may need to review its storage protocols, most importantly looking into updating the guidelines for determining expiry of donated blood.
The team looked specifically at the rate of decay and how any blood units stored for longer than three weeks suffer a severely diminished efficacy, losing the capacity to deliver oxygen to the cells that most need it.
The team, comprised of study leader Steven M. Frank, MD and his colleagues, published their report online in the journal Anesthesia and Analgesia. Rather than focusing on the degradation of nitric acid, the Johns Hopkins researchers focused more on the diminishing elasticity of the red blood cells over time. They believe the flexibility of the cell diminishes significantly the longer a unit is stored. As cell flexibility disappears, the red cells are less able to squeeze into the smaller capillaries to deliver much needed oxygen to tissue. They also found the flexibility of the cell, once lost, is never regained after the transfusion of the unit into a patient.
“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 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.”
The team, in presenting their findings, understands the stress our national blood banks are under in trying to provide fresh blood for everybody. They also acknowledge the implementation of a shorter expiry period may effectively sap the banks blood inventories. But, according to Frank, the current practice of transfusing blood stored up to six weeks may need to be reconsidered.
The Johns Hopkins team, for this latest study, identified and enrolled 16 patients due to have spinal fusion surgery. This specific surgery was selected due to the high likelihood of a patient undergoing this procedure to require a blood transfusion. Of the 16 patients in the study, six received transfusions of five or more units. The remaining ten study participants required three or fewer units of transfused blood. From each unit, 53 in all, the research team drew samples to examine. The findings drawn from this examination showed the samples stored more than three weeks were more likely to contain the less flexible red blood cell membranes.
Additionally, three days post-surgery, the patients provided blood samples for the researchers. Though the blood cells were once again in a biological environment with proper pH, electrolytes and oxygen levels, the cell membrane flexibility of the red cells provided in the older units had not reversed themselves. In fact, the researchers believed the rigidity of the cell membranes to have become permanent. Frank contends the damaged blood cells would likely remain dysfunctional for their life cycle limit. This could be up to 120 days time.
Also interesting to note was that those patients who received fewer units of blood during their surgery had healthier red blood cells overall. This remained true despite their received units having been just as old and presenting cell damage. According to Frank, this is most likely because a small amount of these problem cells make less of a difference than when a large number of damaged cells are present.
In all, the average age of the blood used for transfusion in this study was more than three weeks. Of the 53 units administered, only three samples were found to have been two weeks old or less. Frank points out one important reason for the lack of availability of fresher blood for adults is the industry-wide practice of placing a priority on pediatric patients for the freshest units.
Frank also spoke in detail on the method by which blood banks dispense older blood first so that it won’t exceed its current six week shelf life. “As a colleague said, it’s like how they sell milk in the grocery store – they put the oldest cartons out front so they can sell them before they expire.”
Currently under way are two large randomized controlled studies. Being conducted in both the United States and Canada, the research teams are hoping to definitively determine the relative safety of older versus newer blood. According to those associated with the studies, their findings should be published some time in 2014. Frank, addressing the tenuous nature of our national blood bank system, cautions that these institutions need to be prepared, should the study findings dictate, to change their organizational practice of storing blood for six weeks.