Health insurance is nearing monopoly status in most markets, driving up the cost of insurance, reducing innovation in health care and squeezing doctors and hospitals, an American Medical Association (AMA) report finds.

"The remarkable reduction in the number of competing health plans is troubling for doctors and patients, as competition drives innovation and efficiency in the health care system," said AMA Board Member J. James Rohack, M.D. "Most alarmingly, in the combined HMO and PPO markets, 95 percent of metropolitan areas have few competing health insurers."

In addition, the study found that in 95 percent of markets, a single insurer had a market share of 30 percent or greater, and in 56 percent of the markets, a single insurer had a market share of 50 percent or greater.

The AMA report, Competition in Health Insurance: A Comprehensive Study of U.S. Markets, analyzed 294 metropolitan health insurance markets against an index used by federal regulators for measuring market concentration. According to the federal index, markets that are highly concentrated have few competing health insurers.

"Patients do not appear to be benefiting from the consolidation of health insurance markets," said Dr. Rohack. "Health insurers are posting historically high profit margins, yet patient health insurance premiums continue to rise without an expansion of benefits."

The AMA findings must be viewed in the context of the unprecedented consolidation of the health insurance market, Rohack said. Between 1995 and 2005, there were more than 400 mergers involving health insurers and managed care organizations, according to a researcher of merger and acquisition trends in the health care industry.

"Given the troubling trends in health insurance nationwide, federal regulators need to take a hard look at whether patients are being harmed as mergers and takeovers reduce the number of competing health insurers," said Dr. Rohack. "When it is difficult for a new insurer to enter a market with few dominant health plans, patients can be charged high prices without the threat of competition to keep insurers in check."