Hospitalized patients who received blood that had been stored for more than four weeks were nearly three times as likely to develop infections as those who received fresher blood, researchers said Tuesday.
The blood itself was not infected, but the stored blood's release of chemical agents called cytokines may have affected the recipients' immune systems, rendering them more susceptible to infections, said Dr. Raquel Nahra of Sparks Regional Medical Center in Fort Smith, Ark.
The patients typically suffered an increase in urinary-tract infections, pneumonia and infections associated with intravenous lines, but those who were infected were no more likely to die, Nahra told a Philadelphia meeting of the American College of Chest Physicians.
And although the apparent increase in risk was large, the overall number of infections remained small, she said.
Rules permit blood to be stored for 42 days; then it must be discarded. Blood banks typically use the oldest blood on hand first so that it does not go to waste.
The new study follows a March report that heart-surgery patients who received blood that had been stored for more than two weeks were 64% more likely to die in the hospital than those who received fresher blood.
The differences in the studies highlight "a need for controlled studies on the effect of the age of blood on patient outcomes," said Dr. Richard J. Benjamin, chief medical officer of the American Red Cross.
But, he added, donated blood plays a key role in patient care, and "physicians and patients need to weigh the potential benefits against the small risk of harm caused by transfusion."
The study, conducted at Cooper University Hospital in Camden, N.J., while Nahra was on staff there, included 422 patients in the medical/surgical intensive care unit who received stored blood between July 2003 and September 2006. Overall, 57 patients developed one or more infections while they were hospitalized.
Patients who received blood that was older than 32 days were 2.9 times more likely to develop an infection than those who received blood less than 28 days old, said Dr. David Gerber of Cooper University Hospital, the senior author on the study. Those who received more than five units of blood were also more likely to develop an infection, he said.
The researchers did not investigate the types of organisms involved.
The major limitation in both of the studies was that they were retrospective, meaning that researchers gathered data on patients who had already been treated. It's important now to look at the question prospectively to determine whether the findings can be validated, Gerber said.
Many experts fear that if new regulations are enacted to reduce the time that blood can be stored, less blood will be available. Supplies of donated blood are often short in certain locations and at certain times of the year, and new rules could exacerbate those shortages.
Maugh is a Times staff writer.