Concentration of insurance markets is the topic of a detailed new report from the American Medical Association (AMA), which finds that limited competition between insurers could cause harm to consumers and providers.

The AMA report identified insurers with the largest shares of market of commercial health insurance, Medicare Advantage plans, and public health exchanges that are part of the affordable Care Act (ACA).

"High market concentration tends to lower competition among health insurers, which can harm patients by raising insurance premiums above competitive levels," said AMA President Jesse M. Ehrenfeld, M.D., M.P.H. "The share of markets that are highly concentrated may be far higher than reflected under current federal guidelines. The AMA supports draft federal guidelines that would lower the regulatory threshold for markets to be considered highly concentrated. To reverse the trend toward health insurance consolidation, the AMA strongly supports the [federal] proposal as the proper prescription to scrutinize and potentially limit harmful insurance mergers."