Blue Cross Blue Shield of Tennessee and Vanderbilt University Medical Center reached an agreement this summer to make sure patients could continue paying in-network prices. But that deal didn’t include members using Medicare Advantage.

Those patients will lose in-network status at the end of the year.

Blue Cross Blue Shield and VUMC issued statements, saying the decision to go out-of-network for Medicare Advantage members was mutual. The companies will send patients letters about the split this week. It’s unclear how many patients will be affected.

Each organization says this change won’t affect other Blue Cross members. Neither side explained the falling out.

Medicare Advantage allows private insurance companies to manage coverage for about half of America’s seniors.

But there is a growing trend of medical providers — like hospitals — to drop Medicare Advantage plans.

Becker’s Hospital Review reports at least 25 providers nationwide are dropping Medicare Advantage groups this year. Those include plans under Humana, UnitedHealthcare and Aetna. That list doesn’t include VUMC’s parting with Blue Cross.

Trade groups — like the American Hospital Association — say that insurance companies are more likely to pay late or refuse coverage for Medicare Advantage members.

The association released a report last week, saying denial rates for Medicare Advantage patients were growing more than twice as quickly, compared to patients with traditional private health insurance.