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(Lower Endoscopy)

Procedure overview

Illustration of the anatomy of the digestive system, adult
Click Image to Enlarge

What is a colonoscopy?

Colonoscopy is a diagnostic procedure that allows the doctor to examine the entire length of the large intestine. Colonoscopy can assist in identifying problems with the colon, such as early signs of cancer, inflamed tissue, ulcers, and bleeding. Colonoscopy is also used to screen for colorectal cancer, the second leading cause of cancer-related deaths in the U.S. and the fourth most common cancer in men and women.

An endoscope, which is a long, flexible, lighted tube (also called a colonoscope), is inserted through the rectum into the colon. In addition to allowing visualization of the internal colon, the colonoscope enables the doctor to irrigate, suction, inject air, and access the bowel with surgical instruments. During a colonoscopy, the doctor may remove tissue and/or polyps for further examination and possibly treat any problems that are discovered.

Other related procedures that may be used to assess problems of the colon include abdominal X-ray, computed tomography (CT scan) of the abdomen, abdominal ultrasound, barium enema, and sigmoidoscopy. Please see these procedures for additional information.

Anatomy of the colon

The large intestine, or colon, has four sections:

  • Ascending colon. This extends upward on the right side of the abdomen.

  • Transverse colon. This extends from the ascending colon across the body to the left side.

  • Descending colon. This extends from the transverse colon downward on the left side.

  • Sigmoid colon. This is named because of its S-shape and extends from the descending colon to the rectum.

The rectum joins the anus, or the opening where waste matter passes out of the body.

Screening guidelines for colorectal cancer

Colorectal cancer screening guidelines for early detection from the American Cancer Society recommend that beginning at age 50, both men and women should follow one of the examination schedules below:

  • Annual fecal occult blood test (FOBT) or fecal immunochemical test (FIT) and flexible sigmoidoscopy (FSIG) every five years

  • FOBT or FIT every year

  • FSIG every five years

  • Double-contrast barium enema every five years

  • Colonoscopy every 10 years

People with any of the following colorectal cancer risk factors should begin screening procedures at an earlier age and be screened more often:

  • Strong family history of colorectal cancer or adenomatous polyps in a first-degree relative, in a parent or sibling before the age of 60 or in two first-degree relatives of any age

  • Family with hereditary colorectal cancer syndromes, such as familial adenomatous polyposis and hereditary nonpolyposis colon cancer

  • Personal history of colorectal cancer or adenomatous polyps

  • Personal history of chronic inflammatory bowel disease

Reasons for the procedure

A colonoscopy may be used to examine colon polyps, tumors, ulceration, inflammation, diverticula (pouches), strictures (narrowing), and foreign objects within the colon. It may also be used to determine the cause of unexplained chronic diarrhea or gastrointestinal bleeding or to evaluate the colon after cancer treatment.

Colonoscopy may be indicated when the results of a barium enema and/or sigmoidoscopy warrant further examination of the colon.

There may be other reasons for your doctor to recommend a colonoscopy.

Risks of the procedure

As with any invasive procedure, complications may occur. Complications related to colonoscopy include, but are not limited to, the following:

  • Persistent bleeding after biopsy or polyp removal

  • Peritonitis (inflammation of the lining of the abdominal cavity)

  • Perforation of the intestinal wall (rare)

  • Nausea, vomiting, bloating, or rectal irritation caused by the bowel cleanse prep and/or procedure

  • Adverse reaction to the sedative or pain medication

There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.

Certain factors or conditions may interfere with a colonoscopy. These factors include, but are not limited to, the following:

  • Use of soap suds enemas prior to the procedure, which irritate the lining of the mucosa

  • Presence of barium from previous tests used to examine the colon (such as a barium enema)

  • Inadequate preparation of the bowel before the procedure

  • Problems that may interfere with the passage of the colonoscope, such as narrowing of the colon, surgical adhesions, or disease, such as chronic inflammatory disease

Before the procedure

  • Your doctor will explain the procedure to you and offer you the opportunity to ask any questions.

  • You will be asked to sign a consent form to do the test. Read the form carefully and ask questions if something is not clear.

  • You will be asked to fast for eight hours before the procedure, generally after midnight. You may be given additional instructions about a special diet for one to two days prior to the procedure.

  • If you are pregnant or suspect that you are pregnant, you should notify your health care provider.

  • Notify your doctor if you are sensitive to or are allergic to any medications, latex, tape, and anesthetic agents (local and general).

  • Notify your doctor of all medications (prescribed and over-the-counter) and herbal supplements that you are taking.

  • Notify your doctor if you have a history of bleeding disorders or if you are taking any anticoagulant (blood-thinning) medications, aspirin, ibuprofen, or other medications that affect blood clotting. It may be necessary for you to stop these medications prior to the procedure.

  • Your doctor will instruct you about specific ways to prepare your bowel for the test. You may be asked to take a laxative, an enema, a rectal laxative suppository, and/or drink a special fluid that helps prepare your bowel.

  • Patients with diseases of the heart valves may be given antibiotics before the procedure.

  • A sedative and pain medication will be given to provide relaxation and drowsiness before the procedure. You will need someone to drive you home afterward.

  • Based on your medical condition, your doctor may request other specific preparation.

Illustration demonstrating a colonoscopy, part 1
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During the procedure

A colonoscopy may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.

Generally, the colonoscopy follows this process:

  1. You will be asked to remove any jewelry or other objects that may interfere with the procedure.

  2. You will be asked to remove your clothing and given a gown to wear.

  3. An intravenous (IV) line may be inserted in your arm or hand. A sedative and/or pain medication may be injected into the IV.

  4. Your heart rate, blood pressure, respiratory rate, and oxygen level will be monitored during the procedure.

  5. You will be asked to lie on your left side with your knees bent towards your chest.

  6. A lubricated colonoscope will be inserted into the anus and advanced into the rectum and colon. You may experience mild pain, pressure, and/or cramping during the procedure. A sedative is given to lessen the discomfort.

  7. You may be asked to take slow, deep breaths while the tube is being inserted to relax the abdominal muscles and decrease the discomfort. You may also be asked to change your position to aid the passage of the colonoscope.

  8. Air may be injected into the bowel to aid visualization. In addition, a water jet may be used to cleanse the lining of the colon and a suction device may be used to remove liquid feces.

  9. The doctor will examine the colon and may take photographs. If a polyp is seen, it may be removed, biopsied, or left alone until a subsequent operation is performed.

  10. After the procedure has been completed, the colonoscope will be removed.

After the procedure

After the procedure, you will be taken to the recovery room for observation. Your recovery process will vary depending on the type of sedation that is given. Once your blood pressure, pulse, and breathing are stable and you are alert, you will be taken to your hospital room or discharged to your home.

You may be asked to fast for a few hours and avoid foods high in fiber content for the first 24 hours after the procedure.

You may experience flatulence (passing of gas) and gas pains after the procedure. This is normal. Walking and moving about may help to ease any discomfort.

Alcohol should be avoided for at least 24 hours after sedation. You may be encouraged to drink extra fluids to make up for the water lost during preparation for the procedure.

Notify your doctor to report any of the following:

  • Fever and/or chills

  • Frequent bloody stools

  • Abdominal pain and/or bloating

  • Inability to pass gas

Following a colonoscopy, your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.

Online resources

The content provided here is for informational purposes only, and was not designed to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your doctor. Please consult your health care provider with any questions or concerns you may have regarding your condition.

This page contains links to other websites with information about this procedure and related health conditions. We hope you find these sites helpful, but please remember we do not control or endorse the information presented on these websites, nor do these sites endorse the information contained here.

American Cancer Society

American College of Gastroenterology

American Gastroenterological Association

National Cancer Institute (NCI)

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

National Institutes of Health (NIH)

National Library of Medicine