According to most authorities, if a patient has a clear bill of health after a colonoscopy another isn't recommended for 10 years.  But a review of over 24,000 Medicare cases found that over half of the patients with no reason to have a repeat probing are requested to do so well before that decade is up.  The investigation published in Archives of Internal Medicine found that just under half of the patients who had a colonoscopy had another within 7 years, and half of those people had no clear reason to do so. When the researchers looked at the numbers, they found high-volume colonoscopy centers were more likely to recommend the procedure with no indication for it, and that men who were overweight or had other risk factors were more likely to have another unnecessary colonoscopy before the 10 year window.

This isn't simply a story about the waste in the medical system- at a rate of $362/procedure, the unnecessary colonscopies cost US taxpayers over $2 million for this sample alone.  Colonoscopy isn't without risk.  While a rare complication, one in 1700 patients (so at least 14 in this study, 3 of whom didn't even need the second procedure) end up with bowel perforation during screening.  Bowel perforation can spiral into a nightmare in a hurry, resulting in blood infections or removal of the colon.  Of course, these can happen at the ten year interval, but exposing an older person to that risk more times than necessary is not only a bad practice, it's simply unethical.

It's a good idea for health care providers to help keep track of the dates of all the health screenings their patients undergo, especially for the elderly, and keep up to date on changes in policy recommendations.

James S. Goodwin, Amanpal Singh, Nischita Reddy, Taylor S. Riall, Yong-Fang Kuo (2011). "Overuse of Screening Colonoscopy in the Medicare Population." Arch Intern Med. Published online May 9, 2011. doi:10.1001/archinternmed.2011.212