Blood transfusion during coronary bypass surgery increases risk for infection and death in the first 100 days after surgery, according to an article in the December issue of the American Heart Journal.

If the correlation proves true, it may help explain a longstanding medical mystery: why women bypass patients are more likely than men to die in the first few months after surgery. Women are more likely to receive blood during heart bypass operations.

The study was conducted by the Patient Safety Enhancement Program (PSEP) at the University of Michigan Health System and was based on data from 9,218 bypass patients. After adjusting for factors such as the urgency of the operation, those who received blood transfusions from donors were five times more likely to die within 100 days of their operation than those who did not.

Prior research had shown that recipients of stored donor blood have more post-surgical infections and that women receive more transfusions because they tend to have lower hemoglobin concentrations.

This new study connects the dots. “To the best of our knowledge, this is the first study to state that allogeneic transfusions may be the reason why women have a greater post-bypass surgery mortality risk than men,” said author Mary A.M. Rogers, Ph.D., M.S., PSEP, research director and research assistant professor of internal medicine.

The authors noted that the infections observed in the study are not likely due to contamination of the blood, but are more likely to reflect the patient’s immune response to substances such as white blood cells that are present in stored donor blood. These findings may help guide hospitals and blood banks in deciding whether to filter donated blood to reduce levels of white blood cells. This practice is increasingly common, but not yet universal, in the United States.

The researchers performed statistical analyses that took into account the patients’ blood transfusion status, their co-existing diseases, age, race, sex, and whether the bypass operation was done on an elective, urgent or emergency basis. They looked at infections and deaths that were reported during the 100 days after surgery.

In all, about 88 percent of women received a donor blood transfusion during bypass surgery compared with nearly 67 percent of men. When the researchers adjusted for other factors, women were 3.4 times as likely as men to receive blood. This gender difference was evident regardless of whether the operation was elective, urgent or emergency.

The risk of having an infection of any kind was about three times greater in patients who received donor blood than in patients who did not. The more blood they received, the higher their infection risk. No single type of infection was more common among blood recipients. Overall, 9 percent of women and 6 percent of the men died within 100 days of surgery.

For patients who had banked their own blood and who received only their own blood, the infection risk was similar to that of patients who received no blood transfusions. Rogers noted that patients should ask their doctors regarding banking their own blood if possible, when scheduled for a bypass operation or other surgery.