What is Colonoscopy?

Colonoscopy is a procedure in which a trained specialist uses a long, flexible, narrow tube with a light and tiny camera on one end, called a colonoscope or scope, to look inside your rectum and colon. Colonoscopy can show irritated and swollen tissue, ulcers, polyps, and cancer.

How is virtual colonoscopy different from colonoscopy?

Virtual colonoscopy and colonoscopy are different in several ways. Virtual colonoscopy is an X-ray test, takes less time, and doesn’t require a doctor to insert a colonoscope into the entire length of your colon. However, virtual colonoscopy may not be as effective as colonoscopy at detecting certain polyps. Also, doctors cannot treat problems during virtual colonoscopy, while they can treat some problems during colonoscopy. Your health insurance coverage for virtual colonoscopy and colonoscopy may also be different.

Why do doctors use colonoscopy?

A colonoscopy can help a doctor find the cause of unexplained symptoms, such as

  • changes in your bowel activity
  • pain in your abdomen
  • bleeding from your anus
  • unexplained weight loss

Doctors also use colonoscopy as a screening tool for colon polyps and cancer. Screening is testing for diseases when you have no symptoms. Screening may find diseases at an early stage, when a doctor has a better chance of curing the disease.

Screening for Colon and Rectal Cancer

Your doctor will recommend screening for colon and rectal cancer at age 50 if you don’t have health problems or other factors that make you more likely to develop colon cancer.1

Risk factors for colorectal cancer include

If you are at higher risk for colorectal cancer, your doctor may recommend screening at a younger age, and you may need to be tested more often.

If you are older than 75, talk with your doctor about whether you should be screened. For more information, read the current colorectal cancer screening guidelines from the U.S. Preventive Services Task Force (USPSTF).

Government health insurance plans, such as Medicare, and private health insurance plans sometimes change whether and how often they pay for cancer screening tests. Check with your insurance plan to find out how often your insurance will cover a screening colonoscopy.

Visit the National Cancer Institute to learn more about colon and rectal cancer

How do I prepare for a colonoscopy?

To prepare for a colonoscopy, you will need to talk with your doctor, arrange for a ride home, clean out your bowel, and change your diet.

Talk with your doctor

You should talk with your doctor about any medical conditions you have and all prescribed and over-the-counter medicines, vitamins, and supplements you take, including:

  • aspirin or medicines that contain aspirin
  • nonsteroidal anti-inflammatory drugs such as ibuprofen or naproxen
  • arthritis medicines
  • blood thinners
  • diabetes medicines
  • vitamins that contain iron or iron supplements

Arrange for a ride home

For safety reasons, you can’t drive for 24 hours after the procedure, as the sedatives or anesthesia used during the procedure needs time to wear off. You will need to make plans for getting a ride home after the procedure.

Clean out your bowel and change your diet

A health care professional will give you written bowel prep instructions to follow at home before the procedure. A health care professional orders a bowel prep so that little to no stool is present in your intestine. A complete bowel prep lets you pass stool that is clear. Stool inside your colon can prevent your doctor from clearly seeing the lining of your intestine.

You may need to follow a clear liquid diet for 1 to 3 days before the procedure and avoid drinks that contain red or purple dye. The instructions will provide specific direction about when to start and stop the clear liquid diet. In most cases, you may drink or eat the following:

  • fat-free bouillon or broth
  • strained fruit juice, such as apple or white grape—doctors recommend avoiding orange juice
  • water
  • plain coffee or tea, without cream or milk
  • sports drinks in flavors such as lemon, lime, or orange
  • gelatin in flavors such as lemon, lime, or orange

Your doctor will tell you before the procedure when you should have nothing by mouth.

A health care professional will ask you to follow the directions for a bowel prep before the procedure. The bowel prep will cause diarrhea, so you should stay close to a bathroom.

Different bowel preps may contain different combinations of laxatives, pills that you swallow or powders that you dissolve in water and other clear liquids, and enemas. Some people will need to drink a large amount, often a gallon, of liquid laxative over a scheduled amount of time—most often the night before the procedure. You may find this part of the bowel prep difficult; however, completing the prep is very important. Your doctor will not be able to see your colon clearly if the prep is incomplete.

Call a health care professional if you have side effects that prevent you from finishing the prep.

How do doctors perform a colonoscopy?

A trained specialist performs a colonoscopy in a hospital or an outpatient center.

A health care professional will place an intravenous (IV) needle in a vein in your arm to give you sedatives, anesthesia, or pain medicine so you can relax during the procedure. The health care staff will monitor your vital signs and keep you as comfortable as possible.

For the procedure, you’ll be asked to lie on a table while the doctor inserts a colonoscope into your anus and slowly guides it through your rectum and into your colon. The scope pumps air into your large intestine to give the doctor a better view. The camera sends a video image of the intestinal lining to a monitor, allowing the doctor to examine your intestinal tissues. The doctor may move you several times on the table to adjust the scope for better viewing. Once the scope has reached the opening to your small intestine, the doctor slowly withdraws it and examines the lining of your large intestine again.

A patient lying on their side while a doctor performs a colonoscopy and a depiction of the lower GI tract examined during a colonoscopy (including the colon, rectum, colonoscope, and anus.
© October 2014 Terese Winslow LLC, U.S. Govt. has certain rights. For the procedure, you'll be asked to lie on a table while the doctor inserts a colonscope into your anus and slowly guides it through your rectum into your colon.

During the procedure, the doctor may remove polyps and send them to a lab for testing. Colon polyps are common in adults and are harmless in most cases. However, most colon cancer begins as a polyp, so removing polyps early is an effective way to prevent cancer.

The doctor may also perform a biopsy. You won’t feel the biopsy.

Colonoscopy typically takes 30 to 60 minutes.

What should I expect after a colonoscopy?

After a colonoscopy, you can expect the following:

  • You’ll stay at the hospital or outpatient center for 1 to 2 hours after the procedure.
  • You may have abdominal cramping or bloating during the first hour after the procedure.
  • The sedatives or anesthesia takes time to wear off completely.
  • You should expect a full recovery by the next day, and you should be able to go back to your normal diet.
  • After the procedure, you—or a friend or family member—will receive instructions on how to care for yourself after the procedure. You should follow all instructions.
  • A friend or family member will need to drive you home after the procedure.

If the doctor removed polyps or performed a biopsy, you may have light bleeding from your anus. This bleeding is normal. Some results from a colonoscopy are available right after the procedure. After the sedatives or anesthesia has worn off, the doctor will share results with you or, if you choose, with your friend or family member. A pathologist will examine the biopsy tissue. Biopsy results take a few days or longer to come back.

What are the risks of colonoscopy?

The risks of colonoscopy include

  • bleeding
  • perforation of the colon
  • abnormal reaction to the sedative, including respiratory or cardiac problems
  • abdominal pain
  • death, although this risk is rare

Bleeding and perforation are the most common complications from colonoscopy. Most cases of bleeding occur in patients who have polyps removed. The doctor can treat bleeding that occurs during the colonoscopy right away. However, you may have delayed bleeding up to 2 weeks after the procedure. The doctor diagnoses and treats delayed bleeding with a repeat colonoscopy. The doctor may need to treat perforation with surgery.

A study of screening colonoscopies found roughly two serious complications for every 1,000 procedures.2


October 2014

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This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings through its clearinghouses and education programs to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.