As many as 50% of some appeals prompt health insurers to reverse their decisions, according to a report from the Government Accountability Office. Insurers frequently deny claims due to billing errors, missing information or judgments on whether the care or service is appropriate, the investigative arm of Congress said in a report released Wednesday. These denials can be based on mistakes like an incorrect code on a claim submitted by a doctor's office, said Nancy Davenport-Ennis, CEO of Patient Advocate Foundation, a not-for-profit that helps people appeal claims denials. "You've got a lot of people in America who are ultimately paying a bill they don't owe because they don't realize it's an incorrect code," said Davenport-Ennis, who wasn't involved in the government study. The GAO studied health insurer rejection rates at the request of Congress, which wanted a better picture of the issue as part of the health care overhaul it passed last year.