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. 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 odds of having an infection of any kind were about three times greater in patients who received allogeneic blood than in patients who did not. The more blood they received, the higher their infection risk. This "dose dependent" relationship strengthens the evidence that transfusions may be related to infections. No single type of infection stood out as more common among blood recipients, which suggests a body-wide immune response issue rather than a problem, for example, at the site of the incision.

The analyses revealed that women were more likely to experience an infection than men after bypass surgery, which appeared to be due to the increased number of transfusions in women. This resulted in an increased mortality rate in women. Overall, nine percent of women and six percent of the men died within 100 days of their operation.

For patients who had banked their own blood ahead of the operation and who received only their own blood, the infection risk was similar to that of patients who received no blood transfusions.; Source: Stanford University of Michigan Health System