Doctors, patients and Medicare advocates scrambled on Wednesday to determine how they are affected by UnitedHealthcare's decision to eliminate thousands of doctors from its physician network for Medicare Advantage next year.

The head of the Fairfield County Medical Association, which alerted its members to the change on Tuesday, said the news has shaken up patients and doctors.

"Our telephone has been ringing off the hook," association Executive Director Mark Thompson said in a phone interview Wednesday. "Our fax machine hasn't stopped. In fact, even patients are calling us. Everyone is genuinely — they're very concerned about this."

UnitedHealthcare plans to eliminate 810 primary-care physicians and 1,440 specialists from its Medicare Advantage network in Connecticut next year, the association said. The insurer would not confirm that number Wednesday but said that, in 2014, it will have at least 1,500 primary-care physicians and more than 4,000 specialists in the network.

Thompson, who has been outspoken in his opposition to the move, said UnitedHealthcare is cutting the most expensive doctors, including those with the sickest patients.

"We can tell by the doctors that are contacting us, these are the doctors who are doing, well, kidney dialysis, retina detachments," Thompson said. "These are the doctors who will take the most difficult patients."

"These patients who only have a few months to live, they've got to change their doctor when they're in the last six months of their life? I mean that's how cold and devastating this is," Thompson said.

A UnitedHealthcare executive denied that the insurer was targeting doctors who are most expensive to the system.

"We are assessing our network in Connecticut to help us provide higher quality and more affordable health care coverage for Medicare beneficiaries," Dennis O'Brien, regional president of UnitedHealthcare Networks, said in a an e-mail responding to questions from The Courant.

When asked about Thompson's charge that the insurer is eliminating from the network doctors with the sickest patients, O'Brien wrote, "Absolutely not."

"Ultimately, our goals are to build health care provider networks that encourage better health care outcomes, foster more collaboration between Medicare Advantage plans and physicians, and encourage more use of primary care," O'Brien said.

On Tuesday, a company spokesman said the changes were part of an attempt to build "a network of health care providers that we can collaborate with more closely to have the most positive impact on the quality of care for our members."

"This will encourage better health outcomes and ultimately lower costs," the spokesman said.

Medicare Advantage is a type of health plan funded by the federal government that is available to people 65 and older. It is administered by private insurers and covers Medicare Parts A and B benefits, which is hospital and medical coverage. Additionally, insurers court customers by offering other benefits, such as out-of-pocket cost protection, vision, hearing or dental coverage — none of which is available through traditional fee-for-service Medicare coverage offered by the government, said Robert Zirkelbach, a spokesman for America's Health Insurance Plans, an insurance trade organization.

No List Available

The Fairfield County Medical Association is analyzing which doctors have been cut to see if their patients are in worse medical condition than doctors who are still in the network. It could take weeks to do that analysis, Thompson said, and they are only doing it because UnitedHealthcare would not provide a list of physicians who were eliminated nor would the insurer provide a list of the doctors that remain.

In a letter dated Oct. 2 to doctors dropped from UnitedHealthcare's Medicare Advantage network, the insurer said those doctors will remain a part of UnitedHealthcare's network for commercial health plans. But if the doctors are being eliminated for reasons of "quality," as UnitedHealthcare has said, then Thompson wondered, why are they kept in the commercial plans?

Dr. Bollepalli Subbarao, president-elect of the Hartford County Medical Society, said UnitedHealthcare did not give any advance notice to the state's medical societies about the change.

"We're all kind of in a daze with this situation," he said.

There's already a long waiting list for people to see their doctors, he said. An appointment for a knee surgery, for instance, could take three months.