Overview of Colonoscopy Risks

Risk-Benefit Analysis of Colonoscopies and How to Reduce the Risk

A colonoscopy calendar reminder.
What are the risks and possible complications of a colonoscopy?. Catherine Lane/Getty Images

So, you've heard ad nauseam how great colonoscopies are at preventing colon cancer. But your skeptical side (perhaps egged on by the child in you who insists you don't need screening) says there must be more to the story. Here are some facts to help you decide if the risks from a colonoscopy are worth the benefits.

What Are the Risks of a Colonoscopy?

Colonoscopy risks include heavy bleeding, intestinal perforation (poking a hole in the gut), infection, adverse reaction to the sedatives, and bowel infection.

However, these complications rarely occur and are even less common with colonoscopies that don't involve polyp removal. Risks include (and will be expanded on below)

  • Performation
  • Bleeding
  • Postpolypectomy syndrome
  • Infection
  • Reaction to anesthesia (most commonly cardiac and respiratory complications)
  • Colonscopy prep complications
  • False negative results
  • Rare complications
  • Death

How Often Do Colonoscopy Risk Become Complications?

While minor symptoms such as bloating are common, around 1.6 percent of people experience a complication of colonoscopy serious enough to warrant an emergency room visit or hospitalization. Keep in mind that this includes both those who have polyps removed and those who do not, those who have medical conditions requiring colonoscopy, and those who are older or in ill health. Roughly 85 percent of complications are related to polyp removal.


Perforation is one of the greater fears during colonoscopy.

This can occur when a colonoscope breaks through the bowel lining and into the peritoneal cavity as a result of mechanical means, due to barotrauma, or in the process of removing a polyp. The risk varies from less than 0.01 percent in those who have a screening colonoscopy alone to 0.3 percent in those who have a polyp removed, with an overall risk of 0.05 percent.


Minor and transient bleeding is common following a colonoscopy. The risk of significant bleeding, however, appears to be 2.6 out of a thousand for those who have a colonoscopy alone, up to 9.8 out of a thousand for those who have a polyp removed The risk is somewhat greater for those who have larger polyps removed, for those who have poor bowel preparation, and for those who are taking the blood thinner Coumadin (warfarin.)

Postpolypectomy Syndrome

Postpolypectomy syndrome is a burn injury to to the bowel related to the cautery used when a polyp is removed. It is also called postpolypectomy electrocoagulation syndrome for this reason. The incidence ranges from 3 in 100,000 to 1 in 1000 people (0.003 to 0.1 percent.) Symptoms, which begin one to five days after the procedure, include pain, fever, and an elevated white blood cell count.


Transient bacteremia (bacteria in the bloodstream) occurs in up to 25 percent of people, but this rarely causes any problems. We only mention this for those who have heart valve defects (for example, due to heart murmurs) who should take preventive antibiotics prior to the procedure.The risk of serious infection such as peritonitis (infection in the abdominal cavity) is rare.

Anesthesia Reactions

The sedation given for colonoscopies, sometimes called "twilight sleep" is quite safe relative to deeper anesthesia, but can cause occasional complications. The most common risks are cardiopulmonary, and include hypoxia (a lack of oxygen in the blood), aspiration pneumonia, and heart arrhythmias. Allergic reactions to the sedative medications may also occur. The overall risk of cardiopulmonary complications is around 9 out of a thousand people.

Colonoscopy Prep Complications

Though unpleasant, most people tolerate the preparation for colonoscopy very well. Problems may occur for those with conditions such as congestive heart failure and kidney disease.

False Negatives

A false negative occurs when a disease is present but a screening test fails to detect the disease. If a polyp or colon cancer were present, but not detected on colonoscopy, this would be a false negative. False negative rates vary widely depending on the experience of the physician performing the procedure and the method used for reporting. The overall risk of a false negative result (when someone develops colon cancer despite a normal colon cancer screening test in the preceding three years) appears to be between 3.5 and 7 percent.

Rare Complications

There are several uncommon and rare complications which have been reported after colonoscopy. Some of these include rupture of the spleen and diverticulitis. Gas explosion, which may result from the combination of hydrogen and methane combined with oxygen and electocautery is also a very rare occurrence.


The risk of death related to colonoscopy is very low, estimated at between .007 and .03 percent. A study in 2010 found that of  over 371,000 people undergoing a colonoscopy there were 128 deaths from any cause. Considering that colonoscopies are often done on older people and those with other medical conditions, this number is very low.

Who is at Risk for Complications?

Statistics can give us an idea of "average" risk for complications, but the risk for an individual person can vary depending on many factors. Some things that may raise risk include:

  • Polyp removal - When polyps are found and removed at the time of colonoscopy there is a greater risk for perforation and bleeding than when a colonoscopy is done alone and no polyps are detected.
  • Older age.
  • Other medical conditions - "Cormorbid conditions" such as heart disease increase the risk of complications, especially that of anesthesia.
  • The use of blood thinners - An exception is that of aspirin which did not appear to increase bleeding, but does appear to decrease the risk of heart related complications.

How Can You Minimize Colonoscopy Risks?

Proper colonoscopy prep will help make sure your doctor has a clear view while navigating through your colon. Other suggestions include:

  • Choose a board-certified gastroenterologist to perform the procedure as opposed to your family doctor.
  • Make sure you follow directions for your colonoscopy prep.
  • Make sure an experienced anesthesiologist will be present in case you have an adverse reaction to the sedative.
  • Choose a clinic or hospital that performs a large number of these procedures. Studies suggest that facilities which perform a large number of colonoscopies have a lower complication rate than those which do fewer procedures.
  • Have the procedure in or near a hospital. If bowel perforation occurs, you want to be able to get it repaired right away.

You may also want to ask your doctor if he plans to apply abdominal pressure during the colonoscopy. A study published in Gastroenterology Nursing found that colonoscopy risks, duration, and discomfort could be minimized if the doctor used certain abdominal pressure techniques during the procedure.

Does Colon Cancer Screening Save Lives?

It's important after reviewing the possible complications of colonoscopy to stress that colonoscopy can clearly save lives. Whereas there has been some debate over the effectiveness of breast cancer and prostate cancer screening, colon cancer screening definitely makes a difference, and appears to be responsible for the decreasing rate of death from colon cancer.

Still, colon cancer remains the 3rd leading cause of cancer-related deaths in men and the 3rd leading cause of cancer-related deaths in men.

Colon cancer screening is unique in that it can be used for both prevention and for early detection. When polyps are found and removed in the precancerous stage, colonoscopy can serve a preventive role. When early cancers are found, colonoscopy can serve as a method for early detection.

Weighing the Risks and Benefits of Colonoscopy for Colon Cancer Screening

It's important for everyone to weigh the risks and benefits of colonoscopies for colon cancer screening as it pertains to them personally. The answer for most people will be yes. Colonoscopies are among the most successful tools we have available for preventing cancer. Yet while most often the benefits far outweigh the risks, current guidelines are designed for the "average" person, and nobody is average. For example, there are likely people for whom the risks may instead outweigh the benefits. The only way to be certain is to have a conversation with your doctor. And then, if you choose to have a colonoscopy, take another look at how you can minimize your risks (see above.)


American Society for Gastrointestinal Endoscopy. Complications of Colonoscopy. 2011. http://www.asge.org/assets/0/71542/71544/56321364-c4d8-4742-8158-55b6bef2a568.pdf

Ranasinghe, I., Przynski, C., Searfoss, R., et al. Differences in Colonoscopy Quality Among Facilities: Development of a Post-Colonoscopy Risk-Standardized Rate of Unplanned Hospital Visits. Gastroenterology. 2016. 150(1):103-113.

Reumkens, A., Rondagh, E., Bakker, C., Winkens, B., Masclee, A., and S. Sanduleanu. Post-Colonoscopy Complications: A Systematic Review, Time Trends, and Meta-Analysis of Population-Based Studies. American Journal of Gastroenterology. 111(8):1092-101.

Stock, C., Ihle, P., Sieg, A., Schubert, I., Hoffmeister, M., and H. Brenner. Adverse Events Requiring Hospitalization Within 30 Days After Outpatient Screening and Nonscreening Colonoscopies. Gastrointestinal Endoscopy. 2013. 77(3):419-29.

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