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First-ever large-scale study of colonoscopy complications identifies those Canadians at greatest risk from the procedure


Although colonoscopy has established benefits for the detection and prevention of colorectal cancer, a new study has found that the procedure is associated with risks of serious complications, including death.

The population study by researchers at the Institute for Clinical Evaluative Sciences (ICES) in Toronto, which was published this month in the journal Gastroenterology, is the first large-scale study to examine colonoscopy risks among Canadians.

“Until now, the most widely quoted complication rates for colonoscopy were from case series performed by expert endoscopists,” says lead ICES investigator, Dr. Linda Rabeneck. “Our objectives were to evaluate the rates of bleeding, perforation and death associated with outpatient colonoscopy and their risk factors in a population-based study.”

Researchers analyzed the health system records of 97,204 persons who had an outpatient colonoscopy in four provinces. This is the first study to explore the effects of so-called “endoscopist factors”—such as physician specialty and experience doing colonoscopy—on complication rates.

“We found that older age, male sex, having a polypectomy, and having the procedure done by a low-volume endoscopist were independently associated with colonoscopy-related bleeding and perforation,” says Dr. Rabeneck, who is also Chief of the Odette Cancer Centre at Sunnybrook Health Sciences Centre and Regional Vice-President of Cancer Care Ontario.

The pooled rate of colonoscopy-related bleeding among patients in the four provinces was 1.64 per 1,000 patients; the pooled rate of perforation was 0.85 per 1,000 patients. The mortality rate following colonoscopy (which could only be calculated for Ontario patients) was 0.074 deaths per 1,000 patients (or approximately one death per 14,000).

The study looked at people aged 50 to 75 years who underwent an outpatient colonoscopy between April 1, 2002 and March 31, 2003 in British Columbia, Alberta, Ontario and Nova Scotia. The researchers linked data from these patients with data on all individuals who were admitted to hospital with bleeding or perforation within 30 days following the colonoscopy. (Perforation is defined as a hole in bowel wall which can lead to potentially serious health problems, sometimes requiring corrective surgery.)

The patient factors associated with colonoscopy-related bleeding or perforation were increased age, male sex, and having a polypectomy (removal of suspicious polyps identified during the colonoscopy procedure). Patients whose colonoscopies were performed by the lowest-volume endoscopists (fewer than 300 procedures annually) had three-fold higher odds of bleeding or perforation.

“Until now, we have had scant information and almost no Canadian information concerning risk factors for bleeding and perforation associated with outpatient colonoscopy,” says Dr. Rabeneck. “This information is important given the widespread and increasing use of colonoscopy and the need to evaluate possible harms of the procedure.”

The study, supported by a grant from the Canadian Institutes of Health Research (CIHR), was done in collaboration with researchers from the University of Toronto, the University of Calgary, Dalhousie University in Halifax, Nova Scotia, and the University of British Columbia.

The latest findings have important implications for outpatient colonoscopy practice and health policy, the researchers say. Patients need to be informed of the risks of the procedure, including the risk of death. Endoscopists need to be especially careful in performing polypectomies, and in performing colonoscopy in older men.

Should Canadians, who are encouraged to undergo colonoscopy be alarmed about the study findings? “Absolutely not,” says Dr. Rabeneck. “Colonoscopy is a critical tool in the prevention and early diagnosis of colorectal cancer. But everyone, including patients and doctors, should be aware that this tool needs to be applied with thought and care because of its potential to do harm. One clear take-away message from our research is that people should seek referrals to a high-volume practitioner to perform their colonoscopies.”


Colorectal cancer is the second leading cause of cancer-related deaths in Canada and the US.

Colonoscopy is widely used to detect both colorectal cancer and adenomatous polyps – which may become malignant if left alone. The procedure involves inserting a specialized device called an endoscope through the rectum into the large bowel. Doctors who perform the procedure—typically gastroenterologists or general surgeons—are sometimes referred to as “endoscopists.”

Colonoscopies should meet rigorous quality standards. Cancer Care Ontario’s Colonoscopy Standards set a target of colonoscopy-related perforations of less than one per 1,000 patients for all colonoscopies and less than one per 2,000 patients for screening colonoscopies.

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and is a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.


  • Natalie Chung-Sayers
  • Ph: 416-480-4040


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