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Many times when you go to your doctor and your doctor wants to refer you to a specialist the doctor will recommend a doctor within their medical group. You do not have to settle for that.
If you have a Medicare Supplement your network is the entire United States. You can use any doctor that accepts Medicare in the country.
If something serious develops and you have a serious medical problem, why not find the best doctor. I would ask my doctor who they think is the best doctor to go to. Go online and search for the best doctor in your area. Do your research. When you have found that doctor, then make an appointment. All you have to ask is if they accept Medicare. If they do, then your Medicare supplement will cover you expenses.