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Women's greater risk of dying after coronary artery bypass graft surgery may be due to transfusion-related immunosuppression

Women are more likely to die than men after coronary artery bypass graft surgery (CABG). A new study suggests it may be due to blood transfusion-related immunosuppression. Women tend to have lower hematocrit and hemoglobin than men and therefore are more likely to receive transfusions during surgery. Indeed, the study of Michigan Medicare patients found that women undergoing CABG were 3.4 times as likely to have received blood as men and generally received more units of blood (11.6 vs. 8.1), after accounting for factors such as age, race, and coexisting medical conditions. Patients who received transfused blood were nearly three times more likely to develop an infection than patients who did not (14.6 vs. 4.9 percent).

The prevalence of infection increased with the number of units (U) received during hospitalization from 13.6 percent for 1 to 4 U and 25.3 percent for 5 to 49 U to 30.8 percent for 50 to 99 U and 33.3 percent for 100 U or more. The risk of mortality attributable to female sex was 13.9 percent, but was no longer significant when adjusted for blood transfusion. Also, patients who received a transfusion were 5.6 times more likely to die within 100 days after surgery than those who did not receive a transfusion.

The risks of transmission of various infectious agents from allogeneic transfusion (from another individual with compatible blood type) are generally low. However, the presence of foreign leukocytes in donor blood may suppress the immune system of the recipient. Patients who have received nonleukoreduced blood are at increased risk of postoperative infections and multiorgan failure, explain the Michigan researchers.

They note that the United States has not adopted a universal leukoreduction policy and that by 2003, an estimated 70 percent of the nation's blood supply was leukoreduced. However, their findings were based on analysis of Medicare files of 9,218 Michigan patients hospitalized for CABG surgery from July 1, 1997, through September 22, 1998. The study was supported in part by the Agency for Healthcare Research and Quality (HS11540).

More details are in "Allogeneic blood transfusions explain increased mortality in women after coronary artery bypass graft surgery," by Mary A.M. Rogers, Ph.D., M.S., Neil Blumberg, M.D., Sanjay K. Saint, M.D., M.P.H., and others in the December 2006 American Heart Journal 152, pp. 1028-1034.

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