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Colonoscopy
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Digestive System

Colonoscopy

Colonoscopy, flexible sigmoidoscopy, and virtual colonoscopy are diagnostic procedures used to examine the rectum and colon for abnormalities like polyps or cancer.

What are colonoscopy and flexible sigmoidoscopy?

Colonoscopy and flexible sigmoidoscopy are procedures that let your doctor look inside your rectum and colon (large intestine) using instruments called scopes. These scopes have a light and a tiny camera attached to a long, thin tube. They allow doctors to see inflamed tissue, ulcers, polyps, and cancer.

  • Colonoscopy checks your entire colon and rectum.
  • Flexible sigmoidoscopy checks the rectum and the lower colon (sigmoid colon) only.

What is a virtual colonoscopy?

A virtual colonoscopy, also called CT colonography, is an x-ray test that looks inside your rectum and part of your colon without the use of a scope.

Who needs these procedures?

You may need these procedures to find the cause of unexplained symptoms such as:

  • Bleeding from your anus
  • Changes in your bowel activity, such as diarrhea
  • Pain in your abdomen
  • Unexplained weight loss

Doctors also use these procedures to screen for colon polyps and cancer. If you are not at higher risk for colorectal cancer, providers typically recommend starting screenings at age 45.

How do you prepare?

Preparation involves discussing your health history and medications with your doctor. You must follow bowel prep instructions to clear stool from your colon, which typically includes:

  • Following a clear liquid diet for about one day before the procedure.
  • Avoiding red or purple drinks or gelatin.
  • Taking laxatives (pills, powder, or enemas) as prescribed.
  • For a virtual colonoscopy, drinking a contrast medium the night before.

How are the procedures done?

  • Colonoscopy: Takes 30 to 60 minutes under IV sedation or anesthesia. The doctor inserts a colonoscope to view the colon and may remove polyps or perform a biopsy.
  • Virtual colonoscopy: Takes 10 to 15 minutes without anesthesia. A thin tube inflates the large intestine with air, and x-ray images are taken while you lie on a table.
  • Flexible sigmoidoscopy: Takes about 20 minutes without anesthesia. The doctor inserts a thin tube to examine the lower colon and may perform a biopsy or remove polyps.

What should I expect after the procedure?

You may experience abdominal cramping or bloating for the first hour. Light bleeding is normal if a biopsy or polyp removal was performed. For virtual colonoscopy or flexible sigmoidoscopy, you can return to normal activities immediately. For a colonoscopy, you will need someone to drive you home, and you can expect a full recovery by the next day.

Frequently Asked Questions

You must inform your gastroenterologist about all medications, especially blood thinners (such as warfarin, clopidogrel, apixaban, or rivaroxaban), diabetic medications, insulin, and iron supplements. Iron supplements are typically stopped 5 to 7 days prior because they coat the colon wall. Diabetic medications require dosage adjustments during the clear-liquid phase to prevent hypoglycemia, and anticoagulants are managed under strict medical guidance depending on individual cardiovascular and bleeding risks.
fter sedation wears off (usually 30 to 60 minutes), mild bloating, cramping, and flatulence are normal as your body expels the air or carbon dioxide used to inflate the colon. Most patients can resume a regular diet immediately after discharge unless a large polyp was removed. You must not drive, operate machinery, or make legally binding decisions for the remainder of the day. Most people return to work and full normal routines the day after the procedure.
successful prep results in stool that is completely liquid, translucent, and yellowish or clear, resembling urine or weak tea, without any dark solid matter or thick brown sediment. If your stool is still cloudy, dark brown, or containing solid particles on the morning of your procedure, call your endoscopy center immediately. Inadequate bowel cleansing can obscure small polyps and often requires canceling and rescheduling the test.
Polyp removal (polypectomy) is painless and preventive, eliminating growths before they have the potential to turn cancerous. The tissue is sent to pathology to determine the polyp type (such as hyperplastic or adenomatous) and cellular characteristics. Based on the number, size, and microscopic features of the polyps, your physician will adjust your surveillance interval, typically recommending your next colonoscopy in 3, 5, or 7 years instead of the standard 10-year routine screening interval.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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