Ask the Doctors

Dear Doctor: What are the risks of a colonoscopy? Based on what I know about the procedure, it seems entirely likely that the colon could be damaged.

Dear Reader: Many people share your concerns, especially if they've never undergone the procedure. The first thing you should know is that colonoscopy is the gold standard in colorectal cancer screening. It can locate and remove polyps that may later increase the risk of colon cancer, and it's critical to the diagnosis of colon cancer in its early stages, when the disease is most curable. Colonoscopy may not be perfect, but studies have found decreased mortality rates among people who have a colonoscopy between the ages 50 and 75. That being said, the colonoscopy is not an entirely benign test.

First, there is the bowel preparation necessary to clear the colon. For some people, the medications to empty the bowels can cause abdominal bloating, pain, nausea, vomiting and alterations of the body's electrolytes.

Many patients who undergo colonoscopies are sedated prior to the procedure, and in people with a previous history of heart disease or severe lung disease, the sedatives can lead to abnormal heart rhythms, a drop in blood pressure and a decrease in the blood oxygen level. These problems are rare, but those with heart and lung disease should be aware of the risks.

After the preparation, the gastroenterologist inserts the scope and adds air to distend the colon, an act called insufflation. Here's where the primary risk comes in: The scope and the insufflation of the colon can indeed lead to perforation (tearing) of the colon. Perforations are more likely to occur after the age of 75; the perforation rate is nearly 6 times higher in that age group than in people under 60. Also, people who are ill from other diseases, such as heart failure, diabetes or cancer, have a greater rate of perforation. So, too, do those with diverticula of the colon (small pouches caused by weakness in the colon wall). Removal of a large polyp also increases the risk of perforation. Large perforations require surgical repair, while small perforations can be managed without surgery. Worldwide, perforation rates from a screening colonoscopy occur once in every 1,428 colonoscopies.

Other risks arise from polyp removal -- standard procedure upon their discovery -- because it can cause bleeding, and this risk increases in patients with a bleeding disorder. To reduce the likelihood of bleeding, all patients having a colonoscopy should stop taking any blood thinners several days beforehand.

As for infections, this complication is very rare and is related to defective equipment or improper cleaning of equipment.

The overall death rate from both screening and diagnostic colonoscopies is about 1 in 35,000, and the rates are continuing to decline.

Although there is a risk from colonoscopies, you should be aware that the risk of colon cancer is much higher -- more than 40 cases per 100,000 people each year in the United States -- and the colonoscopy is essential in the diagnosis of this and other colon diseases. If your doctor says you should have one, I would urge you to follow that advice.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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