Blood Transfusions Raise Heart Patients' Infection and Death Risk

Blood transfusions save the lives of millions of heart surgery patients and others each year. But a new study suggests that patients who receive transfusions during heart bypass surgery have a higher risk of developing potentially dangerous infections, and dying, after their operation.

In fact, this increased risk 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, which are performed on more than 465,000 Americans each year.

The findings, from the Patient Safety Enhancement Program (PSEP) at the University of Michigan Health System, are based on data from 9,218 Michigan 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.

The paper is published in the December issue of the American Heart Journal. It builds on a previous U-M analysis that found that a difference in infection rates accounted for the difference in death risk between men and women bypass patients.

The U-M team, with the help of Neil Blumberg, M.D., of the University of Rochester Medical Center, focused on blood transfusions as a contributing factor. Prior research has 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,” says author Mary A.M. Rogers, Ph.D., M.S., PSEP, research director and research assistant professor of internal medicine. Allogeneic is the term for blood from another person.

The authors strongly note that blood transfusions can be life-saving, and that the infections observed in this study are not likely due to contamination of the blood. Rather, they may be due to other factors, including 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 the levels of white blood cells. This practice is increasingly common, but not yet universal, in the United States.

The study is based on analysis of data from all Medicare beneficiaries ages 65 and older who had coronary artery bypass operations in Michigan in a single year.

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.