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New Evidence on Benefits of Colonoscopies

Study Shows Colonoscopy Exam Can Prevent Colorectal Cancer Throughout Colon

Second Opinion

In an editorial published with the study, Weinberg writes that while it is not entirely clear why colonoscopy is not as effective in the right colon, it would be a mistake to conclude that it is ineffective.

He tells WebMD that the newest findings do not necessarily contradict those of the Canadian studies because those studies also showed protection against right-sided cancers when colonoscopies were performed by doctors who had a high polyp detection rate.

Douglas K. Rex, MD, agrees, noting that the Canadian findings may reflect the fact that a large proportion of colonoscopies in that country are performed by surgeons and primary care doctors and not gastroenterologists who specialize in the exam.

A gastroenterologist himself, Rex is a distinguished professor of medicine at Indiana University School of Medicine and he is the co-author of the American College of Gastroenterology’s screening guidelines for colorectal cancer.

“This is a procedure that requires a certain amount of skill,” he says. “But that doesn’t mean that every gastroenterologist does this exam well.”

Two Key Questions Every Patient Should Ask

In the U.S., screening for colorectal cancer is recommended to start at age 50 for people at average risk and at a younger age for those who have an increased or high risk for the cancer.

But Rex says doctors who perform colonoscopies in the U.S. are not required to document the thoroughness of the exam.

This is not the case in Germany, where quality assurance measures have been introduced nationwide.

While it is not as easy for patients in the U.S. to know if they are getting a high-quality colonoscopy, Rex says every patient should ask two key questions when they schedule their exam:

  • What is the polyp detection rate of the practitioner performing my colonoscopy?
  • Can I see documentation that my colonoscopy will cover my entire colon?

Polyps occur in about 25% of men and 15% of women aged 50 and over who have the exam. A rate much lower than this may indicate a less than thorough examiner, Rex tells WebMD.

Likewise, asking for evidence that the colonoscopy covered the entire colon, which may include a photograph of the point of the large intestine furthest from the rectum, known as the cecum, could lead to a more thorough exam.

“Patients can help make colonoscopy better by demanding evidence that the doctor performing the exam has followed these quality measures,” he says.


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