If you have insurance, your insurance needs to cover the treatment recommended by your doctor. In many cases it will be covered without and issue, but some treatments will not be covered in favor of other (usually less expensive) services. Having insurance is usually the only feasible way to get preventative care.
Even with insurance you are often still responsible for a portion of your care, at least until a certain amount. This obligation to pay renews every year in most cases, so even if you reach the limit of your obligation this year, next year you will have to reach it again.
If you are not insured, you will have to pay out of pocket. Hospitals cannot deny you care if you are in an emergency condition, but they are only required to get you to a stable condition. I believe you are still required to pay, but they aren't allowed to deny you care if you can't.
Even with insurance you are often still responsible for a portion of your care, at least until a certain amount. This obligation to pay renews every year in most cases, so even if you reach the limit of your obligation this year, next year you will have to reach it again.
If you are not insured, you will have to pay out of pocket. Hospitals cannot deny you care if you are in an emergency condition, but they are only required to get you to a stable condition. I believe you are still required to pay, but they aren't allowed to deny you care if you can't.