The research, released Monday by the Institute for Clinical Evaluative Sciences, identified men and women aged 50 to 74 who had a first colonoscopy to detect colon cancer in Ontario between January 1999 and December 2003.
Of the more than 331,000 people who had the colonoscopies, 13 per cent of the procedures were incomplete. Patients receiving the incomplete colonoscopies were more likely to be older, more likely to be female or have a history of prior abdominal surgery or pelvic surgery.
The odds of an incomplete procedure were more than three-fold greater for colonoscopies done in private clinics or doctors' offices than for those done in hospital.
"This information is important because it could be used to identify circumstances most likely to lead to incomplete colonoscopy," Dr. Linda Rabeneck, senior author of the study, said in a release.
"Quality improvement programs could then be developed to increase completion rates in a targeted manner, and thus potentially decrease colorectal cancer miss rates."
Rabeneck noted that office-based endoscopy is unregulated - there are no standards for endoscope disinfection, credentials for endoscopists, or monitoring after the use of sedation.
"A potential explanation for the higher rate of incomplete colonoscopies in offices is that the procedures are more likely to be performed with less or no sedation, so more procedures may be abandoned because of patient discomfort," she said.
The study is published in the June issue of the journal Gastroenterology.
