A new study reveals that many older Americans are receiving unnecessary colonoscopies, with Medicare picking up the tab.

Medical guidelines recommend that older patients receive the colon cancer screening once every 10 years. However, nearly half of the Medicare patients in the study received a colonoscopy within seven years of getting normal results from a previous exam.

Furthermore, while most patients 80 years and up no longer require a colonoscopy, one-third of patients in the study over the age of 80 received an exam. For those over 85, the risks involved in receiving a colonoscopy outweigh the benefits and are not recommended. An unnecessary colonoscopy of such a patient might actually do harm.

The cost of a colonoscopy typically runs $1,000 or more. Currently Medicare rules state that the program will not pay for excessive colonoscopies, however, a tiny fraction–a mere 2 percent–of claims submitted for patients without any symptoms was denied. Of the patients who received the repeated colonoscopies, only 27 percent showed symptoms suggestive of cancer.