Higher Female Mortality After Bypass Surgery Explained

A new study suggests that transfusions of donated blood may be a reason for the excess mortality among women after coronary artery bypass graft (CABG) surgery.

Researchers at the University of Michigan (Ann Arbor, USA) studied 9,218 Michigan (USA) Medicare beneficiaries who had CABG surgery from July 1, 1997 through September 22, 1998. Of these patients, 74.8% received an allogeneic blood transfusion during the procedure. Transfusions were more common in women than in men (88.2% versus 66.7%), and 14.6% of those who received donated blood had a subsequent infection, compared with 4.9% of those who did not. Patients who received a transfusion were 5.6 times as likely to die within 100 days of the surgery as those who did not receive a transfusion.

There was a statistically significant dose-response relationship between the number of units of whole blood or packed red cells used and the prevalence of infection. Women had a 13.9% unadjusted risk of death, but when the researchers adjusted for transfusions, it fell to 0.6%, which was no longer significantly different from men. The researchers therefore suggest that the key factor appears to be foreign leukocytes, which can act as an immune suppressant, rendering the patient more susceptible to infection. The study was reported in the December 2006 issue of the American Heart Journal.

"There is recent evidence suggesting that the duration of storage of transfused red blood cells increases both in-hospital and post-discharge mortality risk, but we were unable to determine details regarding blood storage in this database,” wrote Dr. Mary Rogers, Ph.D., and colleagues of the University of Michigan department of internal medicine. "It is possible that either the presence of leukocytes or extended storage of blood components, or both, affect mortality risk.”



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