How long a hospital has been storing blood doesn’t appear to have an effect on mortality, alleviating concerns about whether fresh blood was better for patients who need a transfusion.

The study was published in the New England Journal of Medicine and led by Nancy Heddle, MSc, of McMaster University in Hamilton, Ontario, Canada.

Blood can be stored up to 42 days before transfusion. Earlier studies, as detailed in a related editorial written by Aaron A.R. Tobian, MD, PhD, of John Hopkins University, found no evidence fresher blood was superior to older blood. Concerns remained about red-cell “storage lesion,” however, and suggestions that blood in certain long-term storage conditions may worsen bacterial infections.

For Heddle’s study, the data for more than 20,800 patients with either type A or type O blood who underwent transfusions at four hospitals in three countries was evaluated. Patients were split between a short-term storage group, who received blood which had been stored for 13 days, and a long-term group, receiving transfusion of 23-day-old blood.

The mortality rate was about 9 percent for both groups. When results were expanded by another 4,000 patients to include more blood types, the mortality rate remained the same.

“We did not find a significant difference in the rate of death according to the duration of blood storage among patients in a general hospital population who underwent transfusion,” Heddle and her coauthors wrote.

The findings are consistent with earlier trials referenced by Tobian. What may come next, according to Heddle, is testing transfusions using stored blood near the end of its usable life.

“None of the studies involving humans have been designed to determine whether the transfusion of the very oldest red cells (that is, those stored for 35 to 42 days) affect patient outcomes, a question that remains unresolved,” Heddle and her coauthors wrote.