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Orly Avitzur, medical adviser to Consumer Reports, recently received an anesthesia bill of $1,459.90 for her husband’s colonoscopy. It took her by surprise because she knew that anesthesia for screening colonoscopies (what he was supposed to have had) is now covered by insurance. Before Jan. 1, anesthesia coverage was somewhat murky.

She also knew that the Affordable Care Act requires most private insurance plans and Medicare to fully cover many preventive services, including screening colonoscopy.

That meant they should have had no out-of-pocket costs — no co-payments, coinsurance or deductibles. In this case, the doctors had coded the colonoscopy incorrectly, one of many mistakes that can cause consumers to receive bigger medical bills than they should. According to the American Medical Association, 7 percent of the medical bills in 2013 had errors. Other groups estimate that the figure is much higher. Here are the steps Avitzur took to correct the problem, and what you can do in similar situations:

Inform yourself

Familiarize yourself with what your insurance does and doesn’t cover, and read invoices from your health-care providers and the explanation of benefits from your insurer. Make sure that basic information — such as your name, contact information, policy and ID numbers, and dates of service — is correct.

For preventive services, find out which ones should be fully covered. Two common examples: blood pressure screenings for all adults and diet counseling for adults at higher risk of chronic disease. Get a complete list at www.healthcare.gov/preventive-care-benefits. And be aware that “grandfathered” insurance plans — those that existed before March 23, 2010, and haven’t made significant changes to coverage since then — don’t have to cover preventive tests completely.

Track down the mistake

If you get a surprisingly high bill or one you think should have been covered, contact your insurance company’s customer-service department. Confirm that all of the basic information is correct. If you got a bill for a preventive service such as a cholesterol screening, ask whether it should be covered 100 percent, and if so, why you got a bill. (Also determine whether your insurer falls under the grandfathered rule.)

And last, find out whether your claim was coded correctly by your doctor or his staff; an error can trigger a denial of coverage. In some cases, the diagnostic code or procedure code may be wrong; in others, a critical number may have been omitted.

Ask for and keep copies of test results. When Avitzur’s primary care doctor sent her husband’s results to her, she could see that the test done was indeed a screening colonoscopy; the gastroenterologist and anesthesiologist had billed for a diagnostic test. Insurance payment rules differ for those two types of colonoscopy.

As you proceed, write down the name and contact information of those you speak with, along with the date and substance of the conversation. You can also reach out to your state’s department of insurance for help. Learn more at www.consumersunion.org/insurance-complaint-tool.

Ask for a corrected claim

In most cases, you’ll have to ask your doctor, hospital or outpatient facility to submit a corrected claim. After noticing the billing error, Avitzur called the anesthesiologist and gastroenterologist to tell them the charges were inaccurate. By the end of the day, each had assured her that he would submit corrections to the insurance company.

Of course, it’s best to clarify coverage before a claim is filed. So the next time you schedule a preventive visit, for example, ask whether it will be eligible for no-cost care. And while you’re at that appointment, ask if it is being coded not as a preventive visit but as one where diagnostic care was provided or treatment was done because of something that was found during the exam. (In such a case, you may get a bill you had not anticipated.)

And be prepared: October will bring a new system of diagnostic codes. Expect the number of billing errors to balloon — until doctors and hospitals adapt.

Copyright 2015. Consumers Union of United States Inc.

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.