The complex world of health care reimbursement has led to some very unusual situations that could lead to you, as a patient, ending up with a very large bill for a procedure you assumed was fully covered.

Say you have comprehensive health insurance with a deductible and your primary physician recommends a colonoscopy. You choose a participating gastroenterologist and believe you have done everything necessary to ensure you are covered. Not so.

Most people, even those in health care, are unaware that more and more physicians are not accepting insurance. While services provided by your gastroenterologist are covered by your insurance, the anesthesiologist and the radiologist who participate in the procedure may not be. When signing the consent form (usually presented right before the procedure), you are authorizing your gastroenterologist to use his or her judgment in using ancillary services such as a biopsy evaluation or anesthesia, to provide for your care. These other physicians may not be participating with your insurance plan and bill you at out-of-network rates without your being informed in advance.

Out-of-network rates are what insurance companies agree to pay when a subscriber gets care from a nonparticipating doctor. If you review your health insurance policy, chances are you will find something like this spelled out in your plan document.

Out-of-network reimbursement to physicians and facilities is frequently calculated as a percentage of charges (the sticker price that has no connection to actual cost). Hence, the higher the physicians’ charges, the more they get paid.

Here, the real pain begins. If a nonparticipating provider has participated in your care, that physician is allowed to bill you for what the insurance company did not pay, a technique called “balance billing”—which is not allowed if they accept your insurance.

This could result in very large out-of-pocket costs. While your plan probably has an out-of pocket maximum, it is usually much higher than the in-network deductible, and you thus end up owing much more than the amount you expected.

Imagine what would happen if you were admitted to an emergency room where the ER physician, radiologist, pathologist, plastic surgeon and other medical experts were all nonparticipating?

To keep premiums down, insurance companies can either trim coverage or reduce reimbursements to doctors and hospitals. This encourages many doctors to stop accepting low-paying insurance coverage, or any insurance at all. They earn significantly more if their patients pay up front, and they save time and aggravation by ignoring insurance companies. Another benefit is that they would not need a large and costly billing staff.

Unfortunately, the result is that patients will bear a much larger share of health care costs—while not being able to shop for the best physician and best deal in a transparent fashion.

How can you protect yourself? Ask your physician whether all the specialists involved in your care accept your insurance before you schedule the appointment. Read the fine print on the consent form and note that you do not consent to be cared for by nonparticipating providers. This may not work if no participating providers are contracted to work at the facility where you receive care, but at least it will prompt the discussion.

Finally, get educated about the health care system and the details in your insurance policy. Also, tell your legislators that there are too many middlemen between the physician providing the care and the patient receiving that care.