The average lifetime risk of getting colorectal cancer is approximately 1 in 22 men and 1 in 24 women. Colorectal cancers are the second leading cause of cancer death in the United States. Many of these deaths can be prevented by getting early, regular screenings.

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

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.

Your family history and race may affect your risk of getting colon or colorectal cancer. Certain conditions may also increase your risk, such as:

Talk to a doctor about your specific risk factors while determining when and how often you should have a colonoscopy.

Nothing in life is without some level of risk, including this procedure. However, colonoscopies are done every day and are considered safe. While serious complications and even death may occur as a result of colonoscopy, your chances of getting colon or colorectal cancer far outweigh these possibilities.

Despite what you may have heard, preparing for and having a colonoscopy aren’t especially painful. Your doctor will give you specific instructions on how to get ready for the test.

You’ll need to limit your food intake the day before and avoid heavy or bulky foods. At midday, you’ll stop eating solid foods and switch to a liquid diet. Fasting and drinking a bowel prep will follow the evening before the test.

Bowel prep is essential. It’s used to ensure that your colon is completely free of waste, providing your doctor with a clear view during the colonoscopy.

Colonoscopies are done either under twilight sedation or general anesthesia. As with any surgery, your vital signs will be monitored throughout. A doctor will insert a thin flexible tube with a video camera at its tip into your rectum.

If any abnormalities or precancerous polyps are seen during the test, your doctor will most likely remove them. You may also have tissue samples removed and sent for biopsy.

According to the American Society for Gastrointestinal Endoscopy, serious complications occur in around 2.8 percent of every 1,000 procedures when done in people of average risk.

If a doctor removes a polyp during the test, 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 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 your 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 which 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 of average risk or who are older than 75, provided they had the test at least once during the last decade. Older adults are more likely than younger patients to experience complications or death after this procedure.

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:

  • Fecal immunochemical test. This at-home test checks for blood in the stool and must be taken annually.
  • Fecal occult blood test. This test adds a blood test component to the fecal immunochemical test and also must be repeated annually.
  • Stool DNA. This at-home test analyzes stool for blood and for DNA that might be associated with colon cancer.
  • Double-contrast barium enema. This in-office X-ray also requires prior bowel cleansing prep. It can be effective at identifying large polyps but may not detect smaller ones.
  • CT colonography. This in-office test also uses bowel cleansing prep but doesn’t require anesthesia.

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.