Enlarge By Brandi Simons for USA TODAY Dr. Yogesh Mittal, an orthopedic surgeon in Tulsa, works on a patient who is on Medicare. Some doctors have increased the number of Medicare patients they reject due to low payment rates.  ON MEDICARE  JOIN THE CONVERSATION   Track the latest news about President Obama's administration with The Oval  READ THE LATEST POSTS Read all posts

Recent surveys by national and state medical societies have found more doctors limiting Medicare patients, partly because Congress has failed to stop an automatic 21% cut in payments that doctors already regard as too low. The cut went into effect Friday, even as the Senate approved a six-month reprieve. The House has approved a different bill.

• The American Academy of Family Physicians says 13% of respondents didn't participate in Medicare last year, up from 8% in 2008 and 6% in 2004.

• The American Osteopathic Association says 15% of its members don't participate in Medicare and 19% don't accept new Medicare patients. If the cut is not reversed, it says, the numbers will double.

• The American Medical Association says 17% of more than 9,000 doctors surveyed restrict the number of Medicare patients in their practice. Among primary care physicians, the rate is 31%.

The federal health insurance program for seniors paid doctors on average 78% of what private insurers paid in 2008.

"Physicians are saying, 'I can't afford to keep losing money,' " says Lori Heim, president of the family doctors' group.

The Centers for Medicare and Medicaid Services says 97% of doctors accept Medicare. The agency doesn't know how many have refused to take new Medicare patients, Deputy Administrator Jonathan Blum says. "Medicare beneficiaries have good access to physician services. We do have concerns about access to primary care physicians."

The AARP, the nation's largest consumer group representing seniors, is taking notice. Some U.S. areas already face a shortage of primary care physicians. Policy director John Rother says the trend away from Medicare threatens to make it worse.

States are starting to see a flight from Medicare:

•In Illinois, 18% of doctors restrict the number of Medicare patients in their practice, according to a medical society survey.

•In North Carolina, 117 doctors have opted out of Medicare since January, the state's medical society says.

•In New York, about 1,100 doctors have left Medicare. Even the medical society president isn't taking new Medicare patients.

"I'm making a statement," says Leah McCormack, a New York City dermatologist. "Many physicians are really being forced out of private practice."

Florida has the highest percentage of Medicare patients, and most doctors can't afford to leave the program. But "the level of frustration has been higher this year than I've ever seen it before," says Linda McMullen of the Florida Medical Association.