Colonoscopy is the visual examination of the large intestine (colon) using a lighted, flexible video endoscope. The colon begins in the right-lower abdomen and looks like a big question mark as it moves up and around the abdomen, ending in the rectum. It is approximately 4 feet long. The colon has a number of functions including withdrawing water from the liquid stool that enters it so that a formed stool is produced.

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The flexible colonoscope is a remarkable piece of equipment that can be directed and moved around the many bends in the colon. Video endoscopes have a tiny, optically sensitive computer chip at the end. Electronic signals are then transmitted up the scope to a computer which displays the image on a large video screen. An open channel in these scopes allows other instruments to be passed through in order to perform biopsies, remove polyps or inject solutions.

Reasons for the Exam

There are many types of problems that can occur in the colon. The medical history, physical exam, laboratory tests and x-rays can provide information useful in making a diagnosis. Directly viewing the inside of the colon by colonoscopy is usually the best exam. Colonoscopy is used for diagnosis and often treatment of the following conditions:

  • Colon cancer — a serious but highly curable malignancy
  • Polyps — fleshy tumors which usually are the forerunners of colon cancer
  • Colitis (ulcerative or Crohn’s) – chronic, recurrent inflammation of the colon
  • Diverticulosis and diverticulitis — pockets along the intestinal wall that develop over time and can become infected
  • Bleeding lesions — bleeding may occur from different points in the colon
  • Abdominal symptoms, such as pain or discomfort, particularly if associated with weight loss or anemia
  • Abnormal barium x-ray exam
  • Chronic diarrhea, constipation, or a change in bowel habits
  • Anemia


To obtain the full benefits of the exam, the colon must be clean and free of stool. The patient receives instructions on how to do this. It involves drinking a solution which flushes the colon clean or taking laxatives and enemas. Usually the patient drinks only clear liquids and eats no food for the day before the exam.

Medication Adjustments

The physician advises the patient regarding the use of regular medications during that time. In general, the important medications that might need adjustments are aspirin, clopidogrel (Plavix), warfarin (Coumadin), and insulin. Blood pressure pills should be taken the morning of the procedure with a just a few small sips of water.

The Procedure

Colonoscopy is usually performed on an outpatient basis at an outpatient surgery center. The patient is moderately or deeply sedated. The colonoscope is inserted through the anus and moved gently around the bends of the colon. If a polyp is encountered, a thin wire snare is used to lasso it. Electrocautery (electrical heat) is applied to painlessly remove it. Other tests can be performed during colonoscopy, including biopsy to obtain a small tissue specimen for microscopic analysis.

The procedure takes approximately 30 minutes and is seldom remembered by the sedated patient. A recovery area is available to monitor vital signs until the patient is fully awake. It is normal to experience mild cramping or abdominal pressure following the exam. This usually subsides in 1-2 hours or so.


After the exam, the physician explains the findings to the patient and family. If the effects of the sedatives are prolonged, the physician may suggest an appointment at a later date. If a biopsy has been performed or a polyp removed, the results of these are not available for three to seven days.


A colonoscopy is performed to identify and/or correct a problem in the colon. The test enables a diagnosis to be made and specific treatments to be given. Painless biopsies are usually taken for microscopic analysis. If a polyp is found during the exam, it can be removed at that time, eliminating the need for a major operation later. If a bleeding site is identified, treatment can be administered to stop the bleeding. Other treatments can be given through the endoscope when necessary.

Alternative Testing

Alternative tests to colonoscopy include a barium enema or CT colonography. Study of the stools and blood can provide indirect information about a colon condition. These exams, however, do not allow direct viewing of the colon, removal of polyps, or the completion of biopsies.

Side Effects and Risks

Mild bloating and distension sometimes occur for about an hour after the exam until the air is passed. Serious risks with colonoscopy, however, are very uncommon. One such risk is excessive bleeding, especially with the removal of a large polyp. This can be immediate, or delayed up to two weeks later. In rare instances, a tear in the lining of the colon can occur. These complications may require hospitalization and, rarely, surgery. A diagnostic error or oversight may occur, such as a missed lesion. Other potential risks include allergic or adverse drug reactions to the medications, blood pressure changes and/or cardiac or respiratory problems with the use of sedatives. If you prefer, an anasthesiologist can be present for your procedure to assist in managing these rare complications. The physician and the endoscopy team also have advanced training to deal with these rare complications. Overall, colonoscopy is considered a very safe procedure and is recommended in all persons older than 50.

Due to the sedation, the patient should not drive or operate machinery following the exam. For this reason, someone should be available to drive the patient home.


Colonoscopy is an exam that is performed with the patient sedated. The procedure provides significant information used to determine which specific treatment will be given. In certain cases, therapy can be administered directly through the colonoscope. Serious complications rarely occur from colonoscopy. The physician can answer any questions the patient has.