Mayo Clinic is not scheduling appointments for seniors in certain Medicare Advantage health plans because their insurers haven't negotiated contracts for in-network access to the world-renowned medical center.

The clinic said it stopped making appointments for these patients this winter to address capacity concerns. But the change also hints at a financial dispute over payment rates between Mayo and UnitedHealthcare, the health insurance giant based in Minnetonka.

In recent years, Mayo Clinic has seen significant uptick in patients coming to Rochester with coverage from "non-contract" Medicare Advantage health insurers — so much so, in fact, that clinic officials say the increase threatens to crowd out patients covered by in-network insurers.

"There was not a change in policy, but a change in enforcement due to ensuring Mayo has access for our contracted plans (not just Medicare) and those who truly need Mayo's medical expertise," Karl Oestreich, a Mayo Clinic spokesman, said in a statement to the Star Tribune.

"The impact is to non-contract Medicare Advantage plans. Mayo does not have contracts with these plans so there should not have been any expectation of access to the Mayo Clinic by these plans."

Non-contract Medicare Advantage plans are those in which insurance companies have not negotiated payment rates with Mayo to provide health care services. The clinic is considered out-of-network for enrollees in these plans.

In the past, many with UnitedHealthcare coverage used their out-of-network benefits to receive treatment from Mayo physicians, a company spokesman said in a statement to the Star Tribune. The insurer says it has been negotiating to bring Mayo in-network for its Medicare Advantage subscribers.

"We understand how difficult this situation is for some of our members...," UnitedHealthcare said in a statement. "We are committed to reaching an agreement at an affordable cost for the people we serve."

Clinic officials said that between 2019 and 2021, the number of Minnesota patients coming to Mayo with coverage from non-contract Medicare Advantage insurers nearly doubled — cresting 3,200 people last year.

And that's just patients from Minnesota. During that same two-year period, Mayo also saw a 42% jump in out-of-state patients coming to Rochester with non-contract Medicare plans, for a total last year of more than 7,000 people.

At least half of the growth comes from seniors with UnitedHealthcare coverage, Mayo said.

The clinic says that non-contract Medicare Advantage plans usually reimburse the hospital at a lower rate than contracted plans.

"Mayo is open to entering new contracts, but also must keep in mind the impact on capacity to ensure that we can continue to see those patients (regardless of payer) who are in the greatest need of the care Mayo provides," he said. "We understand that affected patients may be disappointed and frustrated."

Lois Briese says she is "very disappointed" with Mayo and not sure what to do.

The 72-year-old Minnetonka resident has coverage through a UnitedHealthcare Medicare Advantage plan. After her doctor suggested in January that Briese see a specialist at Mayo, she learned from the clinic that she couldn't make an appointment.

Now Briese must decide whether to seek care from a different in-network specialist, or drop the Medicare Advantage plan she likes and pick a new one with in-network access to Mayo.

"I'm in limbo here, trying to figure this out," Briese said.

Networks are a common feature in health plans, often impacting what people pay for medical care. The financial terms under which doctors, clinics and hospitals will provide care to health plan members are negotiated between the insurers and health care providers.

Patients who use out-of-network health care providers usually must pay more in co-pays and deductibles. Typically with Medicare Advantage plans in Minnesota, patients have no problem visiting out-of-network providers, said Chad Levis, an insurance agent who is president of the Minnesota Association of Health Underwriters.

Minnesota seniors have been forced to think more about these networks since 2018 when Medicare Cost health plans — a popular type of coverage with looser network rules — were shut down in most counties. Since then, insurers have pushed their Medicare Advantage plans, which tend to have stricter rules on patient choices.

Among the state's largest Medicare Advantage insurers, Mayo Clinic is out-of-network at UnitedHealthcare, HealthPartners and Allina Health Aetna. As of January, more than 111,000 beneficiaries in Minnesota were enrolled in Medicare health plans from the three companies, according to federal data.

Seniors are currently in the midst of Medicare Advantage open enrollment, so those concerned that their health plan lacks in-network access to Mayo Clinic can make a change, up until March 31, said Kelli Jo Greiner, the Medicare program manager at the Minnesota Board on Aging.

Medicare Advantage is a form of health insurance coverage where seniors elect to receive their government-funded benefits through private managed-care companies. Mayo is in-network for Medicare Advantage plans from Blue Cross and Blue Shield of Minnesota, Humana, Medica and UCare.

Mayo will still see all patients for emergency care. The clinic serves more people with Medicare coverage than any other category of insurance, Oestreich said, and Mayo is one of the nation's largest providers of health care for Medicare beneficiaries.

"The primary issue is capacity, not reimbursement," Oestreich said in a statement. "Mayo simply does not have enough capacity to serve an ever-increasing number of patients. Mayo needs to be good stewards with our contracted plans."

Behind the scenes, Mayo might be wary because UnitedHealthcare's growing Medicare Advantage market share in Minnesota could eventually lead to the insurer taking a dominant position in the state's market — much as United already has across much of the country, said Cheryl Damberg, an economist who specializes in health care payment policy at Rand Corp.

As health insurers get bigger, they have more leverage to set payment rates for hospitals and clinics.

"I suspect that Mayo is saying to United: If you want to send patients to us, you have to enter into a deal that is going to pay us some amount — and United is balking," she said. "United is in a tough spot given expectations of Minnesota residents that they should be able to access Mayo."

Star Tribune staff reporter Mary Jo Webster contributed to this report.