CHICAGO -- As many as one-third of the common medical and surgical procedures performed on Medicare patients are inappropriate, exposing them to risk and straining an already burdened health-care budget, a study concludes.

Some physicians "become very skilled in performing these procedures over the years . . . and come to believe they are effective in areas where a majority of their colleagues would disagree," said Dr. Mark Chassin, principal author of the report in the latest Journal of the American Medical Association.

The study examined the frequency with which Medicare patients underwent three procedures -- coronary angiograms, carotid endarterectomies and upper gastrointestinal endoscopies -- and assessed whether the procedures were appropriate for each patient by weighing benefits against potential harm.

Benefits included increased life expectancy, relieved pain and improved functional capacity. Risks considered ranged from death and severe complications such as heart attacks and strokes to adverse reactions to medication.

By projecting their data across the U.S. population, researchers concluded that $850 million could be pared from the nearly $5 billion spent annually on the three procedures. About 32 million elderly or disabled people are enrolled in the national Medicare health program.

The highest rate of inappropriate use of a procedure was the 32 percent found for carotid endarterectomies, which involve surgical removal of obstructions in the major arteries to the brain, Chassin said.

The mortality rate for carotid endarterectomies averages one percent. If the study's data were applied to that figure, of every 1,000 people undergoing the operation, roughly three would die during inappropriate endarterectomies, Chassin said.

"Our belief is that if doctors were provided with the right kind of educational intervention, this kind of inappropriate use could be curtailed," said Chassin, a senior project director at The Rand Corp., based in Santa Monica, Calif., and a practicing physician in nearby Glendale.

Researchers found coronary angiograms were performed inappropriately in 17 percent of the cases studied. That procedure, which uses X-rays and dye to explore for obstructions in the arteries of the heart, is considered a valuable diagnostic tool for elderly patients with heart disease.

Seventeen percent of the gastrointestinal endoscopies, which involve fiberoptic examination of the esophagus, stomach and upper intestine, also were deemed inappropriate.

"I think the implication for patients is that you must understand there is inappropriate use out there and the way to protect yourself is to become involved in the decision-making process," Chassin said.