The median price for a helicopter air ambulance transport roughly doubled to about $30,000 from about $15,000 over a five-year period, a cost that can be “devastating” to the patients involved, the U.S. Government Accountability Office said in a report released Thursday.

The GAO undertook the study to evaluate concerns about patients being billed for and suffering “devastating financial impacts” for services and providers they often have little or no choice in due to the emergency nature of the transports, according to the report.

The office analyzed data from 2010 and 2014 on prices from the Baltimore-based Centers for Medicare & Medicaid Services and a private health insurance database, along with interviewing 26 stakeholders, including eight air ambulance providers, and officials from CMS and the U.S. Department of Transportation to determine potential actions the federal government could take.

Air ambulance costs paid by Medicare are controlled by a fee schedule, but non-Medicare patients are sometimes billed the balance between what their private health insurer pays and the total billed amount by the air ambulance company. In workers compensation cases, disputes over prices charged by air ambulance providers have led to court challenges centering on whether states can implement fee schedules to control air ambulance costs.

The GAO report found price increases could be tied to market concentration of providers — three large independent providers operate nearly three-quarters of the industry’s total helicopters — and a practice of adjusting prices to receive sufficient revenue from private health insurance to compensate for lower paid transports, such as those covered by Medicare.

Stakeholders responding to the GAO’s inquires proposed actions to address air ambulance pricing issues, including raising Medicare rates, allowing state-level regulation of air ambulance prices, and improving data collection for the purposes of investigations and transparency regarding prices.

The report also made recommendations to the U.S. Department of Transportation to address growing concerns around the prices charged for air ambulance transports, including developing a method to receive air ambulance complaints. Those would include concerns about balance billing; taking steps to make complaint information available to the public; assessing available data and determining what information could assist in the evaluation of future complaints; and considering air ambulance consumer disclosure requirements.

The Transportation Department concurred with all recommendations except the third, saying additional information isn’t needed, according to the GAO’s report.