A colonoscopy is a procedure whereby the large bowel (colon) is examined. It is a relatively safe procedure, and allows for therapeutic interventions. It lasts approximately 20 minutes when done for diagnostic purposes, but therapeutic interventions may prolong the procedure. The endoscopist (person performing the procedure) uses a flexible instrument (colonoscope) that is inserted into the anus and advanced through the entire colon, and possibly a short distance into the small intestine.

Indications for a colonoscopy include:

  • A change in bowel habits, especially if accompanied by gastrointestinal symptoms such as weight loss;
  • A history of blood in the stools or rectal bleeding;
  • Diarrhoea that persists;
  • A family history of colon cancer;
  • Anemia as a result of iron deficiency;
  • As a screening tool to detect polyps and colon cancer at an early preventable or treatable stage, in any person over 50 years of age;
  • A history of colonic polyps or colon cancer;
  • As surveillance in patients with inflammatory bowel disease, such as ulcerative colitis;
  • The medical management of inflammatory bowel disease; and
  • As follow-up investigation for other diagnostic procedures such as an abnormal barium enema.


Specific preparations must be followed carefully to allow for clear vision of the lining of the colon (mucosa). Solid foods are normally avoided for a day before the examination, and patients are advised to take clear liquids. One method used to empty the bowels involves drinking four litres of a non-absorbable solution (for example, Go-Lytely) that causes a self-limiting diarrhea. The somewhat unpleasant taste can be partially masked by flavouring and refrigeration of the solution. The preparation is sometimes regarded as the most unpleasant part of the whole procedure.

Medications such as aspirin and non-steroidal inflammatory drugs may contribute to post-procedural bleeding and must be discontinued before the procedure. Other underlying conditions may require special precautions to be taken, for instance antibiotic prophylaxis in the case of valve lesions of the heart. Other prescription drugs should generally not be discontinued, and your endoscopist should be made aware of all the medications the patient is taking.

To make the procedure pain free and forgettable, conscious sedation is used. This influences your judgement and interferes with your ability to make decisions, in a very similar way to alcohol. Transportation home after the procedure should therefore be arranged, and it is generally not advisable to drive a car for 24 hours afterwards.

What to expect

Before the colonoscopy, written, informed consent is obtained. A combination of a sedative to ensure that the patient is relaxed and a narcotic for pain relief is used for conscious sedation. These drugs are administered directly into a vein through an intravenous catheter inserted into in the arm or hand. The vital signs (blood pressure, heart rate, and blood oxygen level) are monitored before, during, and after the examination. The colonoscopy is performed with the patient in the left lateral position. Most patients do not recall anything of the procedure.

The colonoscope is a flexible tube allowing the doctor to look at a magnified image on a TV monitor. It is possible to see small changes in tissue and to obtain biopsies (small pieces of tissue), remove polyps and introduce or withdraw fluid or air through channels of the instrument. These procedures do not hurt, since the lining of the colon does not sense any pain. Air is introduced through the scope to open up the colon so that the scope can be moved forward and to allow the endoscopist to see.


The patient is closely observed after the procedure until fully awake. It is normal to experience some discomfort after the procedure, such as stomach cramps and bloatedness, as well as feeling groggy. Patients should not return to work that day. Most are able to eat normally after the examination. Patients should ask their physician when it is safe to restart aspirin or blood-thinning medications.


A colonoscopy is normally a safe procedure, with very few complications. However, the following are recognised potential complications:

  • Bleeding from sites where polyps were removed, or biopsies were taken. It is usually minimal and stops quickly, or can be easily controlled.
  • Perforation of the colon where a hole or tear is caused in the bowel due to the examination is a serious complication, but very rare.
  • Other complications include adverse reactions to drugs used during the procedure, and local complications at the site of the drug administration.
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