Transfusions Linked to Higher Female Mortality After CABG

ANN ARBOR, Mich., Dec. 20 -- There may be a causal connection between excess allogeneic transfusions for women during coronary bypass surgery and their higher risk of death after the procedure.

In a cohort study of more than 9,000 patients who had a coronary artery bypass graft (CABG), those who got transfusions were significantly more likely to develop post-operative infections and to die, according to Mary Rogers, Ph.D., of the University of Michigan here.

And women were much more likely than men to get a transfusion, Dr. Rogers and colleagues reported in the December issue of the American Heart Journal.

The finding would explain the observation that female mortality is higher after CABG, because when the researchers adjusted their statistical analysis to account for transfusions, women were no more likely to die than men.

"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," Dr. Rogers said.

Dr. Rogers and colleagues studied 9,218 Michigan Medicare beneficiaries who got CABG surgery from July 1, 1997 through Sept. 22, 1998. Of those, they found, 6,893, or 74.8%, got an allogeneic blood transfusion during the procedure.

Analysis found that:

• Transfusions were more common in women than in men -- 88.2% versus 66.7%.
• 14.6% of those who got transfused donated blood had a subsequent infection, compared with 4.9% of those who did not. The difference was statistically significant at P<0.001.

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 (95% CI 3.7- 8.6).

• 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, at P=0.035 for the trend.
• 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 key factor appears to be foreign leukocytes, Dr. Rogers and colleagues said, which can act as an immune suppressant, rendering the patient more susceptible to infection. In fact, patients who were given their own blood had an infection rate of 5.6%, comparable to the 4.9% among patients who got no blood at all.

Many countries routinely remove leukocytes from blood before transfusion, but the U.S. does not, Dr. Rogers and colleagues noted, although one estimate suggests that 70% of the nation's blood supply is treated to remove the cells.

However, "variation in practice across hospitals persists," the researchers said.

The study was strengthened by its population-based design, Dr. Rogers and colleagues said, but was limited because it is not prospective and did not have details regarding the indication for transfusion, its timing or leukoreduction.

An additional limitations pointed out by the authors "is that data on the quantity of blood were not available for all patients, although a dose-response relationship between units of transfused blood and both infection and mortality has been previously reported, similar to what was found in this study."

"Furthermore," they added, "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. It is possible that either the presence of leukocytes or extended storage of blood components, or both, affects mortality risk."