MONDAY, Oct. 17 (HealthDay News) -- How well you fare after coronary artery bypass graft (CABG) surgery may depend on your blood type, a new study finds.

Patients with AB blood type are 20 percent less likely to die after heart bypass surgery than those with A, B or O blood types, Duke University Medical Center researchers found.

Nearly half the population has type O blood and may be at greater risk for bleeding and blood transfusions after surgery, the researchers said.

The findings from more than 15,000 patients were scheduled for presentation Monday at the American Society of Anesthesiologists' meeting in Chicago.

The reason for the differences in risk could be two proteins in the blood responsible for clotting, the von Willebrand factor (vWF) and Factor VIII (FVIII).

The gene that passes on group O is associated with lower levels of these clotting proteins, explained lead author Dr. Ian J. Welsby and colleagues in a society news release.

A person's blood type is determined by two genes, one from each parent. People with type O blood have two O genes. Some patients have one A or B gene and one O gene (AO and BO), which confer medium levels of the clotting proteins. People with AB blood type have no O genes and the highest level of clotting proteins.

This study found that patients with AB blood have the lowest risk for bleeding after CABG surgery, but further investigation is needed to determine the order of risk for patients with other blood types and whether boosting their vWF levels will improve their outcomes after heart surgery, the researchers said.

Research presented at meetings should be considered preliminary until published in a peer-reviewed medical journal, experts say.

More information

The U.S. National Heart, Lung, and Blood Institute has more about coronary artery bypass graft surgery.