Published May 19, 2025
A colonoscopy is an important screening tool, but it’s also one many people would rather avoid. Some are worried about the prep; others are nervous about what their doctor will find. Understanding the process, as well as possible outcomes, can put people at ease.
“Even though colon cancer is one of the most common types of cancer, it is also incredibly preventable and treatable,” said gastroenterologist Avlin Imaeda, MD, PhD, associate professor of Medicine (Digestive Disorders) at Yale School of Medicine. “Colonoscopy is a great preventive test.”
A colonoscopy is a procedure done under sedation, so the patient is asleep and feels no discomfort. Once the patient is sedated, a colonoscope, which is a long, flexible tube with a light on it and camera, is passed through the colon. A careful exam is done and if polyps are seen, they are removed. Any abnormal findings can be biopsied and sent to a pathologist for review.
Most people find out the results of their colonoscopy as soon as they wake up.
“Endoscopists are good at identifying what they’ve seen,” said Dr. Imaeda. “Therefore, the doctor will come and talk to the patient and tell them what they’ve found.”
Polyps: Polyps are little outgrowths in the lining of the colon and can be caused by a combination of genetic and environmental factors. There are different types of polyps. The most common are tubular adenomas, serrated polyps and hyperplastic polyps.
Tubular adenomas are pre-cancerous and can turn into cancer as they grow larger. Sessile Serrated polyps can also be pre-cancerous but look differently than tubular adenomas. Hyperplastic polyps are generally not pre-cancerous when small and found in the lower part of the colon.
Dr. Imaeda says polyps are almost always removed during a colonoscopy. If a polyp is very large, the patient may be referred to an advanced endoscopist that specializes in removing large polyps, or they may even be referred to a surgeon.
“There is data showing the removal of polyps does reduce the risk of getting colon cancer,” said Dr. Imaeda. “But polyps can be missed during colonoscopy. It’s not a perfect test. So, it does reduce the risk, but it does not reduce the risk to zero.”
Diverticulosis: Diverticulosis is when there are small bulging pouches in the wall of the colon. This is very common and, in most cases, does not impact the patient. Sometimes people with diverticulosis can experience symptoms such as abdominal pain, fever and nausea if diverticulitis develops. Sometimes people can have bleeding from diverticulosis.
Inflammation: Inflammation in the colon may indicate another underlying digestive condition such as Inflammatory bowel disease (IBD), which includes Crohn’s disease and ulcerative colitis. Biopsies of tissue taken during a colonoscopy can help confirm a patient’s diagnosis if they have been experiencing unexplained symptoms.
The follow-up required after a colonoscopy will depend on each person’s family and personal health history. For example, those with average risk should get a colonoscopy every 10 years beginning at age 45. However, those with risk factors such as a close family history of colon cancer may need to get screened earlier and more often.
The frequency of future colonoscopies is also dependent on the findings of the patient’s exam. Someone with pre-cancerous polyps that were removed may need to have a repeat colonoscopy earlier than the standard 10-year timeline.
