An Overview of Colonoscopy Risks

Perforation, Bleeding, Infection, and More

Discussing colonoscopy results.
Discussing colonoscopy results. leezsnow/Getty Images

You've probably heard how great colonoscopies are at preventing colon cancer. The American Cancer Society recommends that starting at age 50, all men and women at average risk for colon cancer should get a colonoscopy every 10 years (or one of the following procedures every five years: CT colonography, flexible sigmoidoscopy, or double-contrast barium enema).

You may be curious about how risky a colonoscopy is. There are several possible complications, and some people are at higher risk for them than others, but the good news is that they are all rare. Learn more about the risks and how to minimize them.

Colonoscopy Risks

Colonoscopy risks include heavy bleeding, intestinal perforation (poking a hole in the gut), infection, adverse reaction to sedatives, and bowel infection. However, these complications rarely occur and are even less common with colonoscopies that don't involve polyp removal. Risks include:

  • Perforation
  • Bleeding
  • Postpolypectomy syndrome
  • Infection
  • Reaction to anesthesia (most commonly cardiac and respiratory complications)
  • Colonoscopy prep complications
  • False negative results
  • Extremely rare complications (such as rupture of the spleen, diverticulitis, and gas explosion)
  • Death

How Frequently Complications Occur

While minor symptoms such as bloating are common, only around 1.6 percent of people experience a colonoscopy complication that is 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.

Take a closer look at each possible complication.

  • Perforation: 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.
  • Bleeding: Minor and transient bleeding is common following a colonoscopy. The risk of significant bleeding, however, is 2.6 out of 1,000 for those who have a colonoscopy alone, up to 9.8 out of 1,000 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 the bowel that's related to the cautery used when a polyp is removed. It is also called postpolypectomy electrocoagulation syndrome. The incidence ranges from three in 100,000 to one in 1,000 people (0.003 percent to 0.1 percent.) Symptoms, which begin one to five days after the procedure, include pain, fever, and an elevated white blood cell count.
  • Infection: Transient bacteremia (bacteria in the bloodstream) occurs in up to 25 percent of people, but this rarely causes any problems. Those who have heart valve defects (for example, due to heart murmurs) 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, which is sometimes called "twilight sleep," is quite safe relative to deeper anesthesia, but it 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 nine out of 1,000 people.
  • Colonoscopy Prep Complications: Though colonoscopy prep is unpleasant, most people tolerate it very well. Problems may occur for those who have 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 considered a false negative. False negative rates vary widely, depending on the experience of the physician who is performing the procedure and the method that's 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) is between 3.5 percent and 7 percent.
  • Extremely Rare Complications: There are several extremely rare complications that 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 electrocautery, is also a very rare occurrence.
  • Death: The risk of death that's related to colonoscopy is very low, estimated at between .007 and .03 percent. A study in 2010 found that of more than 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.

    What Increases Your Risk for Complications

    Statistics provide an idea of the average risk for complications, but the risk for an individual person can vary depending on many factors. Some specific things that raise your risk include:

    • Polyp removal: When polyps are found and removed at the time of colonoscopy, there is a greater risk for perforation and bleeding, compared with when a colonoscopy is done alone and no polyps are detected.
    • Older age
    • Other medical conditions: "Comorbid conditions" such as heart disease increase the risk of complications.
    • The use of blood thinners: An exception aspirin, which doesn't increase the risk of bleeding, but does decrease the risk of heart-related complications.

    Minimize Colonoscopy Risks

    Proper colonoscopy prep will help make sure that your doctor has a clear view while navigating through your colon. Other ways to minimize the risk of complications include:

    • Choose the right doc: Pick a board-certified gastroenterologist to perform the procedure, as opposed to your family doctor.
    • Be meticulous: Make sure you follow the directions exactly during your colonoscopy prep.
    • Ask for backup: Make sure an experienced anesthesiologist will be present during the procedure in case you have an adverse reaction to the sedative.
    • Be picky about location: Choose a clinic or hospital that performs a large number of these procedures. Studies suggest that facilities that perform a large number of colonoscopies have a lower complication rate than those that 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.
    • Ask about abdominal pressure: Ask your doctor if he or she 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 uses certain abdominal pressure techniques during the procedure.

      Why Colon Cancer Screenings Save Lives

      After reviewing the possible complications of colonoscopy, it's important to stress that colonoscopy can clearly save lives. Though there has been some debate over the effectiveness of breast cancer and prostate cancer screenings, colon cancer screening definitely makes a difference and is responsible for the decreasing rate of death from colon cancer. Still, colon cancer remains the third leading cause of cancer-related death in men.

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

      Should you get a colonoscopy? The answer for most people is yes because the potential benefits far outweigh the risks. Colonoscopies are among the most successful tools available for preventing cancer. However, talk to your doctor about your particular risk factors in case you have a higher risk for complications than the average person. 

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