A new study by US researchers found that patients given transfusions of blood stored for more than 4 weeks were nearly three times as likely to develop urinary-tract infections, pneumonia and infections associated with intravenous lines, as those getting fresher blood.

US researchers looked at the rate of hospital infections in 422 patients against the age of the blood transfusion they received. The average age of the blood was 26 days, with 70 percent of patients receiving blood older than 21 days, the researchers found. Current federal regulations allow blood to be stored up to 42 days.

Overall, 57 patients developed one or more blood stream infections while they were hospitalized and 11 percent of the patients died. Patients that received blood that was older than 42 days were 2.9 more likely to develop one or more infections, including pneumonia, upper respiratory infection, sepsis and/or shock, than those who received fresher blood.

David Gerber, D.O., study co-author and associate director of the medical/surgical intensive care unit at Cooper University Hospital in Camden, N.J., who presented the results at the American College of Chest Physicians conference in Philadelphia, said that any change to the time limit of 28 days could lead to blood stream infections. The blood itself wasn’t infected, but it degraded over time.

After two weeks, stored red blood cells experience changes that promote the release of biochemical substances called “cytokines” that can lower a patient's immune function and render them more vulnerable to infection, the researchers explained. High levels of cytokines could make patients more predisposed to infection.