Patients transfused with red blood cells (RBCs) more than 14 days old are more likely to have complications or die than patients who get fresher blood, new study results show. The results suggest that storing blood for as long as 6 weeks, which is acceptable under current FDA guidelines, may jeopardize the safety of some patients.

In the study, researchers looked at the records of about 6,000 patients who received blood during cardiac bypass surgery, valve surgery, or both. Almost half of the patients received blood that had been stored for 14 days or less (average, 11 days); the remaining patients received older blood (average, 20 days). All patients received similar amounts of blood.

The 1-year survival rate was 93% for those who got fresher blood and 89% for those who got older blood. Patients who got fresher blood also had lower rates of complications than those in the older blood group.

Patients who received older blood were more likely to develop renal failure, sepsis or septicemia, or multiple organ failure, or to need endotracheal intubation for more than 72 hours after surgery. A composite of complications was more common in patients given older blood than newer blood (26% versus 22%). These findings echo those of smaller studies involving patients undergoing surgery for various conditions.

Why older blood is linked to complications may be related to several factors, including progressive functional and structural changes that reduce oxygen delivery at the tissue level. In addition, RBCs become more rigid during storage, so they don't flow as easily through the body.

The researchers stopped short of calling for an immediate change in blood storage policy. An editorial accompanying the study noted that "it is just not feasible to shorten storage time significantly without restricting the blood supply."

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