It seems so unfair. You’re most likely to get hit with a big medical expense your insurance won’t cover when you’re most powerless to do anything to avoid it.

These surprise medical bills usually result from emergency situations or when your doctor uses out-of-network specialists without telling you, according to a national study by Johns Hopkins University.

The new study, which examined the problem of surprise medical bills, was published today in the Journal of the American Medical Association.

“These are not doctors you typically choose,” says Gerard Anderson, the study's senior author and a professor at the Johns Hopkins Bloomberg School of Health.

As a result, you usually don't know beforehand whether they take your insurance. Anderson says people are shocked when they get a bill for many hundreds or thousands of dollars from out-of-network doctors they may never have met, sometimes months after being treated.

“This is happening all the time," he says.

The study of more than 400,000 doctors across the U.S. ranks the difference between how much Medicare reimburses for treatments the doctors perform and what they charge out-of-network patients covered by other types of insurance—or who aren’t covered at all.

Medicare fee schedules were used as the benchmark because insurers typically use them as a starting-off point when they calculate how much they will reimburse patients for treatments they receive out of network.

The average physician charges about 2½ times what Medicare pays, but the highest markups were for doctors you usually don’t select for yourself—often because it's an emergency or it's a specialist your in-network doctors refers you to.

Who Charges the Most—and Least

The study looked at physician charges across 54 specialties. It found that the average anesthesiologist, radiologist, emergency physician, pathologist, and neurosurgeon charge for their services at least four times what Medicare reimburses. In anesthesiology, the average charge was almost six times as high as what Medicare pays.

On the positive side, doctors with the lowest markups are the ones people see most often. General practice doctors, psychiatrists, allergists, immunologists, dermatologists, and family practitioners charge less than twice the Medicare rates.

The researchers also found regional differences. Doctors in Alaska and Wisconsin, for example, mark up prices at almost twice the rate of doctors in Hawaii and Michigan, on average.

Changes and Solutions

Consumer Reports actively advocates for changes to protect consumers from out-of-network bills, particularly in emergency situations. CR has collected more than 4,000 stories from consumers struggling to pay these bills.

“The study validates what we’ve heard from thousands of consumers—that surprise medical bills are likeliest when a patient is least likely to choose a doctor or be informed of a physician’s network status,” says Betsy Imholz, special projects director and a surprise-medical-bill expert at Consumer Reports.

Imholz says the problem is only growing worse as our healthcare system grows more complex and more insurance companies narrow the network of doctors they contract with or shift to insurance plans that eliminate coverage for out-of-network services.

Consumer Reports has worked with consumer advocacy organizations in several states that have enacted laws barring out-of-network balance billing for services at in-network hospitals. Balance billing leaves the consumer on the hook for what the insurer doesn’t cover by an out-of-network doctor. Since 2015, California, Connecticut, Florida, and New York have passed laws against surprise medical billing.

But Anderson says the problem needs federal action. He thinks Congress should require physicians to tell patients their insurance network status before treating them and should post their out-of-network prices where they can be easily seen. But because “you aren’t thinking of asking whether a doctor takes your insurance when you have a medical crisis,” disclosure alone won’t solve the problem, Anderson says.

There is some Congressional interest in change. In December, Sen. Bill Nelson, D-Fla., asked the Federal Trade Commission to look into surprise medical bills in emergency room situations where patients are treated at in-network hospitals by out-of-network doctors. Consumer Reports also supports national legislation—the End Surprise Billing Act, introduced by Rep. Lloyd Doggett, D-Texas—which protects consumers from balance bills in emergency situations. Doggett plans to reintroduce the bill this year.

Also, Imholz says she expects several states, including Georgia, Utah, and Washington, to introduce legislation to protect consumers from surprise billing this year. “This issue is not going away," she says.

How to Avoid a Surprise Medical Bill

If you have no choice but to use a doctor who’s not in your insurance network, here’s what to do:

1. Talk to Your Doctor
Let your doctor know which insurance you have and ask to be referred only to other doctors in your network if you need a specialist. For other services, such as lab tests or MRIs, find out which providers are in-network and ask the doctor to use them. If you must go to an out-of-network doctor, don’t be afraid to negotiate with him or her. Many are willing to charge you less than their full fee when they don’t have to go through an insurer, says Claire McAndrew, private insurance program director at Families USA.

2. Call Your Health Insurer Before You Go out of Network
Some insurers will cover a portion of out-of-network charges, so find out what your plan offers. If your insurer doesn’t cover anything out of network, ask whether it will make an exception. Explain why you are unable to see an in-network provider for the care you need. If you get an exception, make sure you get necessary approval in writing in advance.

3. Understand What Is Covered in an Emergency
Ask your insurer for documentation on what the plan will and won't cover if you need emergency care. Your insurer can also tell you which area hospitals take your insurance. You can then ask the billing department at your hospital of choice whether the ER doctors participate in your insurance plan. Know that if you call 911 and have the presence of mind, you can request a particular hospital. But it's the ambulance staff’s call which hospital you’ll go to, and they’ll choose the closest facility that’s properly equipped to treat you.

At the hospital, you (or a family member or friend who goes with you) will need to fill out admission forms. This is the time, if it's possible, to request an in-network doctor or other service provider. At discharge, make sure you or your companion requests and keeps all paperwork, including an itemized printout of fees if you have to fight charges later.

4. Fight the Bill
If you get an out-of-network bill, contact your insurer first to see whether it will cover it. If it won’t, try to negotiate the charge with the doctor. If the doctor won't negotiate, file an appeal with your insurance company. The Patient Advocate Foundation offers guidance on how to appeal at no charge. Professional claims consultants will also help for a fee or a percentage of the amount reimbursed. You can find claims consultants via the Alliance of Claims Assistance Professionals or the National Association of Healthcare Advocacy Consultants. If you still get no satisfaction, file an appeal with your state insurance commission.

To find out how to file appeals at the state level and share your story, go to Consumer Reports’ End Surprise Medical Bills site.

More from Consumer Reports:
Top pick tires for 2016
Best used cars for $25,000 and less
7 best mattresses for couples

Consumer Reports has no relationship with any advertisers on this website. Copyright © 2006-2017 Consumers Union of U.S.