IOWA CITY (AP) -- Emergency room doctors who are the most fearful of malpractice suits are more likely than their colleagues to order tests and admit patients for chest pain or other heart symptoms, according to a study led by a University of Iowa researcher.

The study found that such doctors admit even those patients who are low risks for actual problems, said Dr. David Katz, an associate professor of internal medicine at Iowa.

"The fear of malpractice accounts for a significant portion of the variability in what doctors do in the emergency room," Katz said.

The findings were based on a surveys of 33 emergency room doctors who participated in a study of 1,134 patients at two teaching hospitals. The results appear in the July 13 online issue of the Annals of Emergency Medicine.

Nearly 7 million Americans seek emergency care for heart-related symptoms each year, according to the university's school of medicine. Almost half of those patients are admitted to the hospital, yet it's later found that most did not have a serious problem such as a heart attack or unstable angina.

With so many patients involved, Katz said his study could contribute to an understanding of how the practice of "defensive medicine" can increase health care costs.

"Emergency room physicians must see all patients, regardless of how risky a patient's case may be," Katz said. "One way physicians may respond to this is by seeking consultations and admitting patients they are uncertain about."

After surveying emergency room doctors, Katz's team put them into high-, medium- and low-fear groups for malpractice. By analyzing patient records, the researchers determined that doctors with the greatest fear were more likely to admit low-risk patients and order chest X-rays and tests.

Katz said that while the $150 cost of a chest X-ray is a relatively minor expenses, "the volume of patients getting them really raises the overall price tag."

"However, the greatest cost is the cost of admission, which can be as high as $1,200 per patient for a brief hospitalization," he added.

Katz said hospitals can reduce fears of malpractice in their emergency rooms by adding equipment that improves patient safety and reduces the risk of medical errors. University Hospitals, he said, has a chest pain observation unit the can help doctors more accurately identify high-risk patients who require hospitalization.