A colonoscopy at a doctor's office or private clinic is three times more likely to be incomplete than one done in hospital, indicates a study of Ontario patients who took the test that examines the large intestine.

Dr. Linda Rabeneck, a senior scientist at Toronto's Institute for Clinical Evaluative Sciences, and her colleagues found that of more than 331,000 people who had their first colonoscopies, 13 per cent were incomplete.

"This information is important because it could be used to identify circumstances most likely to lead to incomplete colonoscopy," said Rabeneck, also a gastroenterologist at Sunnybrook Hospital in Toronto.

"Quality improvement programs could then be developed to increase completion rates in a targeted manner, and thus potentially decrease colorectal cancer miss rates."

A colonoscopy — consisting of a flexible tube with a camera on it — detects early signs of colorectal cancer, a malignant tumour that develops over at least a decade and usually on the wall of the large intestine.

The researchers, reporting in the June issue of the journal Gastroenterology, analyzed health database information on men and women aged 50 to 74 who had a colonoscopy in Ontario between January 1999 and December 2003.

They said the odds of an incomplete procedure were 3.57 times greater for procedures in a private office than at an academic hospital.

Ask for a gastroenterologist, researchers suggest

"Endoscopists need to be particularly careful to ensure that patients who are older, female, or have a history of abdominal or pelvic surgery have complete procedures," the researchers wrote, given that the results suggest these groups are more likely to have an incomplete procedure. 

"And if a patient does not know the volume of procedures performed by their physician, then they should request a gastroenterologist," who, the study suggests, is least likely to perform an incomplete colonoscopy, Rabeneck recommended. 

In many Canadian cities, there has been a rapid growth of office-based colonoscopies because of reduced access in hospitals, particularly academic ones, the study's authors said.

One reason there's a greater chance of an office colonoscopy being incomplete is little or no sedation may be used, resulting in patient discomfort that stops the procedure, the team speculated.

Office colonoscopies are unregulated in Ontario, meaning no set standards for sedation.

A study published earlier this year by Rabeneck's team concluded women and older individuals are also at higher risk of new or missed colorectal cancers.

In 2006, colorectal cancer was the second leading cause of cancer-related deaths in Canada behind lung cancer. It's expected that about 20,000 new cases will be diagnosed this year, and about 8,700 Canadians will die, according to Canadian Cancer Statistics 2007.