WEDNESDAY, Nov. 16, 2016 (HealthDay News) -- As if a trip to the ER isn't traumatic enough, many U.S. emergency room patients end up with major unexpected costs, a new study says.

Yale University researchers looked at 2.2 million ER visits made by patients younger than 65 nationwide between early 2014 and late 2015.

Nearly one-quarter of the patients who went to ERs within their health insurance networks were treated by an out-of-network doctor and ended up with unexpected expenses, the study found.

According to the findings, out-of-network emergency doctors charged up to 800 percent of Medicare rates, while in-network emergency physicians were paid around 300 percent of Medicare rates.

Patients were presented with an average bill of about $622, and potentially much more, if their insurer only covered in-network rates, the researchers reported.

Many patients would be hard-pressed to pay such a bill, the researchers said. They estimated that 47 percent of Americans could not cover an unexpected $400 expense without incurring credit card debt or selling assets, according to the U.S. Federal Reserve.

"Most patients with health coverage go to in-network emergency rooms and rightly expect to be treated by in-network doctors," said study co-author Zack Cooper, an assistant professor of public health and economics at Yale.

"Our study shows that nearly a quarter of people who visited in-network emergency rooms were exposed to potentially major costs. This is just wrong and we must do better. People should not face financial ruin from medical bills they cannot reasonably avoid," Cooper said in Yale news release.

Based on the findings, Cooper's team believes that state policies on surprise out-of-network billing are inadequate and the federal government has taken no action on the issue.

The researchers suggested that hospitals should be required by law to sell an emergency care package that includes physician services and facility fees. The hospital would then staff its own emergency room and pay the doctors directly.

However, two groups representing ER doctors took issue with the findings.

Dr. Rebecca Parker is president of the American College of Emergency Physicians (ACEP). She said the conclusions from the new study are based on "claims data from a large insurance company, which [is] not identified and not available for examination, showing the lack of transparency by the health insurance industry.

"Most emergency physicians prefer to be 'in-network,' as long as insurance companies pay fairly," Parker said in an ACEP statement.

Besides calling on insurance companies to release more transparent data, she believes that "state and federal policymakers need to ensure that health insurance plans provide fair payment for emergency services and provide adequate rosters of physicians."

Dr. Tim Seay is chair of the Emergency Department Practice Management Association, another trade group. In the same statement, he said the new research "ignores the fact that emergency physicians provide care without regard to the ability to pay. The problem is inadequate insurance coverage and high deductibles."

The study was published Nov. 16 in the New England Journal of Medicine.

More information

The American College of Emergency Physicians has more on emergency room costs.