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Colonoscopy Prep and Procedure

What Is a Colonoscopy Procedure?

A colonoscopy is a procedure to look at the inside of the colon. The colon is the large intestine and the last part of the digestive system. The colon dries, processes, and eliminates the waste left after the small intestine has absorbed the nutrients in food. The colon is about 3 to 5 feet long. It travels from the lower right corner of the abdomen (where the small intestine ends) up to the liver, across the body to the spleen in the upper left corner and then down to form the rectum and anus.

The doctor will use an instrument called the colonoscope to perform a colonoscopy. It is a long (about 5 feet), thin (about 1 inch), flexible fiberoptic camera that allows the doctor to visualize the entire colon.

A doctor may order a colonoscopy to investigate many different diseases of the colon.

Colonoscopy is best known for its use as a screening tool for the early detection of colorectal cancer.

  • Colorectal cancer is the second leading cause of cancer deaths in the United States.
  • Colon cancer develops from growths within the wall of the intestine such as polyps or tumors.
  • These growths often take 5 to 10 years to develop and may not cause many symptoms.
  • A person may not have any symptoms of colon cancer, but having a close relative with the disease increases the risk for the disease compared to the general public.
  • Most people develop polyps after age 50, so the American College of Gastroenterology (the digestive specialists) recommends screening examinations every 10 years for early detection and removal of these cancer-causing growths after that age.

Colonoscopy is also used to investigate other diseases of the colon.

  • Colonoscopy may be used to find the place and cause of bleeding as well as to check areas for irritation or sores in the colon.
  • These colon problems can cause unexplained changes in bowel habits.
  • Pain, bloody diarrhea, and weight loss can be caused by inflammation of the bowel, which may be the result of Crohn's disease or ulcerative colitis.
  • These inflammatory digestive diseases tend to occur in young adults and, if undetected, can produce chronic symptoms and increase the risk of colon cancer.

Colonoscopy is used when there is concern a disease of the colon may exist.

  • The doctor may recommend this test if other screening tests such as a manual rectal examination, a fecal occult blood test (a test that detects blood in the feces), or a barium enema (a test in which barium is used to make the colon visible on an X-ray) suggest that further information is needed to make a diagnosis.
  • A colonoscopy may be required when symptoms of digestive disease or other warning signs are present.
  • Rectal bleeding (which may appear as bright red, very dark, or black)
    • Pain in the lower abdomen
    • Changes in bowel habits
    • Non-dietary weight loss
  • A new test called Cologuard, a stool-based colorectal screening test that detects the presence of red blood cells and DNA mutations, may indicate the presence of certain kinds of abnormal growths that may be cancers such as colon cancer or precursors to cancer. If this test reveals the possibility of colon cancer, a colonoscopy may be necessary.

Only doctors who specialize in the study of digestive or rectal diseases, have special training in endoscopy, and are certified to perform colonoscopy qualify to perform this procedure.

  • The American Society for Gastrointestinal Endoscopy suggests that a doctor perform at least 200 procedures to become technically competent at diagnostic colonoscopy.

Pictures of the Colon and Diseases of the Colon

Patient Comments

Pictures of a Healthy Colon and Diseases of the Colon

Picture of the anatomy of the colon
Picture of the anatomy of the colon

Picture of Colon Cancer and Colon Polyps

Picture of colon cancer
Picture of colon cancer and colon polyps

Picture of Diverticulitis (Diverticular Disease)

Picture of diverticulitis
Picture of diverticulitis

Picture of Crohn's Disease

Picture of Crohn's disease
Picture of Crohn's disease

Picture of Ulcerative Colitis (UC)

Medically Reviewed by a Doctor on 9/11/2017
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Patient Comments & Reviews

The eMedicineHealth doctors ask about Colonoscopy (Prep, Risks, and Side Effects):

Colonoscopy - Describe Your Experience

Please describe your experience with a colonoscopy.

Colonoscopy - Reasons

What was the reason for your colonoscopy? If you were diagnosed with a bowel disease or problem, please share your experience because it may help others with your condition.

Colonoscopy - Procedure

How did you prepare for your colonoscopy procedure?

Colonoscopy - Side Effects

What side effects, if any, did you have after your colonoscopy procedure?

Colon Cancer Symptoms and Signs

Colon cancer, also referred to as colorectal cancer, occurs when cancer cells form in lining of the colon or rectum. In the early stages of colon cancer there often are no symptoms. As the cancer progresses through the large intestine, symptoms and signs may begin appear, for example:

  1. Diarrhea
  2. Constipation
  3. Changes in the color of your stools
  4. Blood in the stools
  5. Weight gain
  6. Fatigue

Read What Your Physician is Reading on Medscape

Colonoscopy »

Colonoscopy enables visual inspection of the entire large bowel from the distal rectum to the cecum.

Read More on Medscape Reference »

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