The American Medical Association (AMA) addressed its concern to major insurers on their practice of rating physicians for patients to choose doctors insurers consider to be offering the best care for the lowest price.

The nation’s largest doctor group sent a letter, signed by 47 state medical societies, to national insurers that use physician rating for health plan products including WellPoint, UnitedHealth, Aetna and Cigna.

As the insurers are competing to offer cheaper coverage to millions of Americans as health reform rolls out, the practice of making patients pay more to use doctors rated as less efficient by insurers could spread, doctors worry.

The main concern reflected in the AMA’s letter is that the ratings are often inaccurate and some physicians’ reputations are being “unfairly tarnished using unscientific methodologies and calculations."

A recent study by RAND Corp. showed that the ratings can be wrong more than 25 percent of the time. Also, the AMA says physicians who are deemed expensive may be looking after sicker patients.

“Patients are being encouraged, and often incentivized, to leave longstanding relationships with physicians they trust,” the AMA wrote in the letter.

Health insurers say that the system is independent and includes input by a variety of parties, even the rated physicians themselves.