Potential Risks of a Colonoscopy

Overall, colonoscopy is a very safe test, and concerns over complications aren't usually a valid reason for putting one off or avoiding one altogether. However, as with any medical procedure, complications are possible (although rare). Studies estimate the overall risk of complications for routine colonoscopy to be low, about 1.6%. In contrast, the lifetime risk for developing colo-rectal cancer is about 4-5%. To put it into perspective: a person's average risk of developing colon cancer is higher than having a complication after a colonoscopy.

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Some of the complications that can occur during a colonoscopy include perforation (a hole in the intestine), bleeding, postpolypectomy syndrome, reaction to anesthetic, and infection.

The purpose of this article is to educate patients about all aspects of a colonoscopy, which does include a tiny amount of risk. The low amount of risk should be reassuring, especially given the importance of this screening test and in its importance in detecting and preventing colorectal cancer. If a colonoscopy is needed, the potential risks described here should not, in the least, be a deterrent, but rather should give patients confidence about the safety of this procedure.

Colonoscopy Preparation Complications

Before a colonoscopy, it is important to clean the bowel properly so that the physician doing the test can pass the instruments through the colon and get a good look at the colon wall. This means emptying the colon of stool, and it's done in a variety of ways in the day or two before the test.

Complications during the prep for a colonoscopy are uncommon, but can occur, particularly in elderly patients, in those with kidney failure, or in those with congestive heart failure.

Risk of Perforation

A perforation is a tear or a hole in the intestine. During a colonoscopy, a physician may remove any polyps (outgrowths on the colon wall) that are found. The risk of perforation is very low after a colonoscopy in which no polyps were removed, and is only slightly higher after a colonoscopy during which a polyp is removed. A perforation can occur if an instrument punctures a thin point in the colon wall, or if the air introduced into the colon during the test causes too much distention.

A large, visible perforation is an emergency and is treated through surgery to close the tear. In some cases with smaller tears that are found early, surgery may not be needed, and the perforation may be treated with bowel rest, antibiotics, and careful watching.

Risk of Bleeding

Bleeding occurs in about 1 out of every 1,000 colonoscopy procedures. The bleeding may be treated during the test, but in most instances, the bleeding will go away on its own.

The risk for bleeding after a polypectomy is a little higher. This type of bleeding may also go away on its own, but it may require treatment if it becomes severe. The bleeding risk is also slightly higher in patients taking blood thinners ( e.g., Plavix, Coumadin, Eliquis), so it is important to discuss with your doctor the need to hold these medications prior to colonoscopy.

Postpolypectomy Syndrome

This is a syndrome that occurs as a result of a burn to the bowel wall during polyp removal. As a reaction to polypectomy, anywhere from 12 hours to a few days later, a patient develops fever, abdominal pain, and an elevated white blood cell count after a colonoscopy. The risk of postpolypectomy syndrome after a colonoscopy during which a polypectomy was done is very low. Treatment may include rest, intravenous fluids, and antibiotics.

Effects From Anesthetic Medications

Sedating medications, often called "twilight sleep," are given during a colonoscopy in order to make patients more comfortable. There are risks, such as an allergic reaction or respiratory problems, any time sedatives are given for a procedure. During a colonoscopy, there is a very small risk of a serious respiratory effect from medications. Other risks from sedatives include a reaction at the injection site, nausea, vomiting, and low blood pressure.

Risk of Infection

Infection after a colonoscopy is very rare. An infection can be transmitted between patients if the endoscope is not cleaned and sterilized properly between tests. The risk of this happening, however, is very low.

A Word From Verywell

A colonoscopy is a safe procedure. The best way to find out what the risks are is to discuss it with the physician doing the test. In most cases, especially when the colonoscopy is being done to screen for colon cancer, the risks are lower than the risk of developing cancer. Risks are typically not a reason to avoid having a colonoscopy. Patients have a right to ask about the risks of a colonoscopy and the preparation: the answers should be reassuring.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.