The day of the test, the patient is restricted to drinking clear, nonalcoholic liquids up to two to four hours before the exam. After that point, the patient may not consume any liquids or take any medications until the procedure is finished.

The colonoscopy may take place in a hospital or in an outpatient office. The procedure is performed by a gastroenterologist, a physician with expertise in gastrointestinal disorders.

Although a properly performed colonoscopy produces little discomfort, patients are given sedatives that sometimes may be combined with pain medication. The patient will have an intravenous (I.V.) line placed for delivery of these drugs. The medications will cause the patient to be either fully asleep or very drowsy and comfortable throughout the procedure. Many patients find that the sedative will prevent them from remembering much of the test.

During the procedure, patients lie on their left side on a table. The physician will lubricate a gloved finger and perform a digital rectal exam. A long colonoscope is then lubricated and inserted into the rectum. This tube – which is about the width of a finger – has a fiber–optic light and a tiny video camera on its tip that the physician uses to search for abnormalities. If awake, the patient may feel a desire to have a bowel movement. This is normal and should not cause concern.

The physician can also send air into the tube channel that inflates the colon, providing a clearer view of its interior lining. As this air enters the colon, the patient may feel cramping or a sense of fullness. However, this discomfort is likely to be minor. Patients can reduce the discomfort by taking slow, deep breaths.

The colonoscope is gently inserted further into the colon until the physician can see the entire colon. The camera at the end of the colonoscope captures images that are transmitted to an external monitor. If an abnormality is discovered, the physician can insert an instrument into the colonoscope channel and perform one of several options:

• Remove the growth
  
  
• Take a biopsy of the abnormal tissue to be sent to a laboratory for analysis
  
  
• Inject solutions or cauterize (destroy) the abnormal tissue

If bleeding occurs during removal of a polyp or other tissue, a laser, heater probe, electrical probe or special medicine can be delivered through the colonoscope to stop the bleeding. In some cases, the physician may decide to wait and remove an abnormality during a separate procedure.

A colonoscopy exam typically takes between 15 minutes and an hour, and research suggests that physicians who spend at least six minutes looking for abnormalities during an initial screening tend to have better results.