Between 2001 and 2110, Medicare has been billed increasingly for office visits at higher-paying codes, an investigation by the nonprofit Center for Public Integrity shows.

The study of over 360 million claims finds the percentage of office visits billed at the highest-reimbursing codes grew from 25% in 2001 to 40% in 2010, according to the Washington Post. Defenders of the shift say that the Medicare population has become older, but research doesn’t bear that out. This so-called “upcoding” cost Medicare an extra $11 billion over the decade studied.

One problem, according to analysts, is that reviewing a claim can cost about as much as the overcharge itself (roughly $40).

Emergency-room billings are also showing upcoding. One researcher characterized the defense that ER patients are presenting sicker as “total nonsense.”

Source: Washington Post