Despite what you may have heard, preparing for and having a colonoscopy may be annoying and uncomfortable, but it isn’t painful.

While all procedures have some risk, colonoscopies are done every day and are considered safe. In fact, your chances of getting colon or colorectal cancer far outweigh the possibility of complications from a colonoscopy.

But that being said, it’s important to remember that there are still risks, even if they’re rare. Read on to learn more about possible colonoscopy risks, as well as what to look for after surgery, and when to speak with your doctor.

A colonoscopy is a screening test used to detect and prevent colon and colorectal cancers. They can also help determine the cause of gastrointestinal conditions, such as chronic diarrhea or constipation, and rectal or abdominal bleeding.

While colonoscopies have their risks, it’s worth repeating that the chances of facing complications that come from not having one are, relatively, much greater.

The average lifetime risk of getting colorectal cancer is approximately 1 in 23 men and 1 in 25 women. Colorectal cancers are the second leading cause of cancer death in the United States.

On the other hand, the American Society for Gastrointestinal Endoscopy says that there are less than 3 serious complications for every 1,000 procedures done in people of average risk for colorectal cancer.

Many of the deaths related to colorectal cancer can be prevented by getting early, regular screenings. It’s recommended that people with average cancer risk start getting this test at age 45 or 50, and every 10 years afterward, through age 75.

Talk to a doctor about your specific risk factors while determining when and how often you should have a colonoscopy. They will help you to prepare for the procedure and answer any questions you may have.

While a colonoscopy in itself is relatively safe, there are several factors that could contribute to problems during the procedure. If a doctor removes a polyp during the test, for example, your chances of complications may increase slightly.

While very rare, deaths have been reported following colonoscopies, primarily in people who had intestinal perforations occur during the test.

Choosing the outpatient facility where you have the procedure may impact your risk. One study showed a marked difference in complications, and quality of care, among facilities.

Risks associated with colonoscopy include:

Perforated intestine

Intestinal perforations are tiny tears in the rectum wall or colon. They can be made accidentally during the procedure by an instrument. These punctures are slightly more likely to occur if a polyp is removed.

Perforations can often be treated with watchful waiting, bed rest, and antibiotics. Large tears, however, are medical emergencies that require surgical repair.


If a tissue sample is taken or a polyp removed, you may notice some bleeding from your rectum, or blood in your stool a day or two after the test.

This is typically nothing to be worried about. However, if the bleeding is heavy, or doesn’t stop, let your doctor know.

Post-polypectomy electrocoagulation syndrome

This very rare complication can cause severe abdominal pain, rapid heart rate, and fever after a colonoscopy.

It’s caused by an injury to the bowel wall that results in a burn. These rarely require surgical repair, and can usually be treated with bed rest and medication.

Adverse reaction to anesthetic

All surgical procedures carry some risk of negative reactions to anesthesia. These include allergic reactions and respiratory distress.


Bacterial infections, such as E. coli and Klebsiella, have been known to occur after colonoscopy. These may be more likely to happen at medical centers that have inadequate infection control measures put in place.

Colonoscopy risks for older adults

Because colon cancer grows slowly, colonoscopies aren’t always recommended for people who are older than 75 and have medical problems that put them at higher risk for complications.

The bowel prep used can sometimes be of concern for seniors because it can lead to dehydration or electrolyte imbalance.

People with left ventricular dysfunction or congestive heart failure may react poorly to prep solutions containing polyethylene glycol. These may increase intravascular water volume causing complications such as edema.

Prep drinks containing sodium phosphate might also cause kidney complications in some older people.

It’s vital that older people completely understand their colonoscopy prep instructions, and are willing to drink the full amount of prep liquid required. Not doing so could result in lower completion rates during the test.

Based on underlying health conditions and health history in older adults, there can also be an increased risk for heart- or lung-related events in the weeks following a colonoscopy.

You’ll most likely be tired after the procedure. Since anesthesia is used, you may be required to have someone else take you home. It’s important to watch what you eat after the procedure so as not to irritate your colon and to avoid dehydration.

Postprocedure problems may include:

  • feeling bloated or gassy if air is introduced into your colon during the procedure and it starts to leave your system
  • a slight amount of blood coming from your rectum or in your first bowel movement
  • temporary light cramping or abdominal pain
  • nausea as a result of the anesthesia
  • rectal irritation from the bowel prep or the procedure

Any symptom that causes concern is a good reason to call a doctor.

These include:

  • severe or prolonged abdominal pain
  • fever
  • chills
  • severe or prolonged bleeding
  • rapid heart rate

Colonoscopy is considered the gold standard of screening tests for colon and rectal cancers. However, there are other types of tests that might be appropriate for you.

These tests typically require colonoscopy as a follow-up if abnormalities are uncovered. They include:

  • Stool tests (every year). There are different types of tests using a stool sample you provide for analysis. The guaiac-based fecal occult blood test (gFOBT) and the fecal immunochemical test (or FIT test) look for blood in the stool, while the FIT-DNA test looks for altered DNA, which may be a sign of cancer.
  • Sigmoidoscopy (every 10 years). This is a less-invasive test that is similar to a colonscopy, but it only enters the last third of your descending colon, or the sigmoid colon.
  • Virtual colonoscopy/CT colonography. This noninvasive test uses X-ray imaging and computers to generate images of the colon without physical contact.

Colonoscopies are highly effective screening tools used to detect colon cancer, rectal cancer, and other conditions. They’re very safe, but not completely without risk.

Older adults might experience higher levels of risk for certain types of complications. Talk to a doctor to determine if you should have a colonoscopy.