Colonoscopy is the most effective tool available for both preventing colorectal cancer and evaluating digestive symptoms. Using a flexible scope with a high-definition camera, your gastroenterologist examines the lining of the entire colon and rectum — roughly five feet of tissue — in a procedure that usually takes under an hour.
What makes colonoscopy uniquely valuable is that it both finds and treats. When precancerous polyps are discovered, they can be removed during the same procedure — stopping colorectal cancer before it ever develops. No other screening test does this.
A stool test can suggest that something may be wrong. A colonoscopy can find the problem and remove it in the same visit — which is why it remains the gold standard.
Why colonoscopy matters
Colorectal cancer is one of the most common cancers in the United States, and one of the most preventable. It almost always begins as a small, benign growth called a polyp, which can take years to turn cancerous. Remove the polyp, and you remove the cancer that would have followed.
Because early colorectal cancer typically causes no symptoms, screening is something you do when you feel completely well. Waiting until something feels wrong often means waiting too long.
When to start
For people at average risk, screening should begin at age 45. You may need to start earlier if you have:
- A family history of colorectal cancer or advanced polyps
- A personal history of polyps or colorectal cancer
- Inflammatory bowel disease, such as Crohn's disease or ulcerative colitis
- A known genetic syndrome, such as Lynch syndrome
- Symptoms such as rectal bleeding or a persistent change in bowel habits, at any age
What colonoscopy is used for
- Routine colorectal cancer screening
- Surveillance after prior polyps or with a family history
- Evaluating rectal bleeding or blood in the stool
- Investigating persistent changes in bowel habits or chronic diarrhea
- Assessing for inflammatory bowel disease
- Evaluating unexplained abdominal pain or iron-deficiency anemia
How to prepare
The colon must be thoroughly cleansed so its lining can be clearly seen. That means a bowel preparation the day before — a prescribed solution along with dietary restrictions. It is widely considered the least pleasant part of the process, and it is also essential: a poorly prepared colon can hide a polyp and force the exam to be repeated.
Your physician's office provides complete, step-by-step instructions specific to your prep and your medical history. Follow them exactly, and ask about adjusting any medications, particularly blood thinners.
See prep instructions and forms →
What to expect
Colonoscopy is an outpatient procedure performed under sedation administered by a board-certified anesthesia team. Most patients rest through it and remember little to none of it. Afterward, you'll recover from sedation at the center, and because of the sedation, you'll need a responsible adult to drive you home. Most patients resume normal activity and eating the next day, and sometimes the same evening.
Your results
Your physician can often share initial findings once you're awake. If a polyp was removed or a biopsy taken, the tissue goes to pathology, with those results typically following within one to two weeks. A normal colonoscopy at average risk generally means a ten-year interval before the next one; if polyps were removed, your physician may recommend returning in three to five years.