Ann Arbor, MI - A new study has shown that patients who receive blood transfusions while hospitalized for coronary artery bypass graft (CABG) surgery are more likely to develop an infection after surgery and are at a greater risk of death than those who do not receive a blood transfusion [1].

These findings, say investigators, could help shed light on why women fare worse after surgery than men. As women receive more blood transfusions than men, primarily because of their lower hemoglobin or hematocrit levels, this might explain the difference in death rates between the sexes following CABG.

"Our results suggest that one mechanism by which women experience more infections (and subsequent mortality) during hospitalization for CABG surgery is a complication of nonleukoreduced allogeneic blood transfusion," write lead author Dr Mary Rogers (University of Michigan, Ann Arbor) and colleagues in the December 2006 issue of the American Heart Journal. "In this population evaluated, women received more blood transfusions than men, and those patients who received transfusions were more likely to experience infection at any site."

In their paper, the authors note that the risk of transmission of various infectious agents from allogeneic transfusion is low, but the foreign leukocytes in donor blood may suppress the recipient's immune system. Patients who receive non-leukocyte-reduced blood are at an increased risk of postoperative infections and multiorgan failure, and many countries, although not the US, have policies in place for the universal leukocyte depletion of allogeneic blood, write Rogers and colleagues.

Because women receive more blood transfusions than men, primarily because transfusion decisions are based on hemoglobin or hematocrit levels, which are lower in women, investigators sought to examine the effect of transfusion on differences in infection and mortality in 9218 Medicare beneficiaries >65 years old in Michigan who underwent CABG between 1997 and 1998.

Overall, women were significantly more likely to receive a blood transfusion, regardless of the urgency of the procedure. After adjustment for age, race, comorbidities, and the urgency of admission, women were 3.4 times more likely to receive blood than men. Those who received a transfusion were approximately 2.8 times more likely to have an infection, the investigators report, with those receiving more blood at greater risk.

Investigators found that the risk of infection and mortality attributable to being female was 19.3% and 13.6%, but this was no longer statistically significant when they adjusted for blood-transfusion status. Overall, 9% of women and 6% of the men died within 100 days of the operation, with those who received a transfusion 5.6 times more likely to die within the 100 days if they had received blood.

Rogers and colleagues acknowledge that the relationship between allogeneic blood transfusion and infection is controversial, with some arguing that confounding variables explain the association. However, "the presence of a dose-response relationship, supportive animal model and mechanistic data, magnitude of the increased risk (up to 10-fold in heavily transfused patients), and the partial abrogation of the effect by use of leukoreduced or autologous transfusions have convinced others that this relationship is real," they write.

The group suggests that an assessment of the risks and benefits of nonleukoreduced blood components and consideration of alternatives are needed, something that is particularly important for women, as they receive disproportionately more blood transfusions when hospitalized.