Colonoscopy Preparation and Procedure

Colonoscopy is a medical procedure in which doctors use a flexible camera to visually examine the colon for polyps, tumors, and other abnormal growths that could lead to serious medical problems such as colorectal cancer.  Colonoscopy can also be used to assist in the diagnosis of Inflammatory Bowel Disease (IBD), diverticulosis, and other more rare forms of colitis.  The American Cancer Society recommends that all men and women get a colonoscopy, or similar gastrointestinal screening procedure, every 10 years beginning at the age of 50.  Those with a family history of colon cancer or early colon polyps should be screened earlier (at least 10 years before the earliest age of diagnosis.)  Although many types of medical doctors administer colonoscopies, they are typically performed by gastroenterologists, colorectal surgeons, and proctologists.

Colonoscopy Procedure

In order to conduct a colonoscopy, the doctors use a colonoscope, which is a type of endoscope, to visually examine the length of the colon and distal portion of the small intestine.  The colonoscope is a flexible tube that is a centimeter in diameter, or about the size of the small finger, that has suction, air, and a fiber optic camera.

During the colonoscopy procedure the doctor will place the colonoscope in the rectum to examine the colon using a computer that is connected to the colonoscope’s camera for inflammation, bleeding, tumors, ulcers, polyps, or other types of abnormal growths.  If the doctor notices any abnormalities in the colon lining during the procedure he or she may perform a polypectomy by using specialized equipment through the channels of the colonoscope to remove polyps or other growths.  These growths are then tested to determine if they are cancerous or precancerous through a biopsy, which will be read by a pathologist and normally resulted within 1-2 weeks after the procedure.

What is a Colonoscopy Like?

Colonoscopies rarely cause much pain and typically take between 15 minutes and 1 hour to complete.  To begin the procedure, patients are given a gown and instructed to lie on their left sides.  The doctor will usually first perform a digital rectal examination, and then will inspect the anus for any blockage before slowly moving the colonoscope through the length of the colon.

Most colonoscopies are done under moderate sedation, or mild anesthesia.  This medication is normally provided by the endoscopist and is always monitored closely by a nurse or tech who is in the room throughout the entire procedure.  Patients who have underlying severe anxiety, heart or lung diseases and history of chronic pain medication use should notify their doctors prior to undergoing this procedure, as alternatives such as deep sedation can be offered under the care of an anesthesiologist.

Since the colon is curved and has many turns, the doctors will distend the colon by injecting air or water through the colonoscope to avoid damaging the colon wall.  After reaching the end of the colon the doctor will begin the actual examination since it is easier to examine the bowel lining while the scope is slowly removed from the colon.  The patient may experience some mild discomfort during the passage of the colonoscope through the colon, especially around sharp turns; however, severe pain is not common.

Because the colonoscope is less than the diameter of an average stool, patients typically find it painless although distending the colon with air sometimes causes discomfort. Usually patients don’t feel anything even if a polypectomy is performed by the doctor.

Regular deep breathing throughout the colonoscopy procedure can prevent cramping and help the patient to relax.  Patients may be asked to change positions and may have the urge to pass gas during the procedure, which is completely normal.  Passing gas throughout the procedure is typically encouraged, and patients should rest assure that no stool will pass should they pass gas.

Colonoscopy Preparation

Although the colonoscopy procedure itself may seem uncomfortable, many patients attest that the colonoscopy preparation is actually more trying than the actual procedure.  Preparation for colonoscopy usually takes 1 to 2 days. During this preparation period, patients typically must stay at home in order to use the bathroom frequently.

Throughout the preparation for colonoscopy, patients must cleanse their colon of all solid foods.  In order to fully cleanse the colon, patients must stop eating solid foods 1 to 2 days in advance of the test and can only drink clear fluids such as apple juice, chicken broth, lemonade, and water.  The typical recommendation is not to eat any foods that you can not clearly see through as ingestion of solid foods may interfere with the results of the colonoscopy and can sometimes necessitate repeat examination or early termination of the exam.  Generally, bowel preparations require ingestion of at least 4 liters of laxative.  Commonly this is all taken the night before the procedure over a 3 hour time course, but split dosing has also been done in which the patient will take the first 3 liters the night before and the final liter 6 hours prior to the procedure to improve yield from the exam.

Oftentimes, colonoscopy doctors will prescribe a laxative or other type of colon prep that causes loose and infrequent stools and sometimes diarrhea. When preparing for a colonoscopy patients are urged to drink plenty of clear fluids to avoid dehydration although dairy products or liquids with that are purple, red, or orange in color should be avoided.  In general, after completion of the bowel preparation, the patient’s stool should be clear and look similar to urine in clarity and consistency.

Colonoscopy is considered the ‘gold standard’ for diagnosis of colon polyps and detecting colorectal cancers.  Like all tests in medicine, it does have a small chance of missing early polyps, polyps hidden behind large folds in the colon, and smaller/flat polyps that may be hidden behind stool if the preparation is not adequate.

Colonoscopy Complications

Like all medical procedures, there are small complications that can result from undergoing colonoscopy.  These complications include risk of missed pathology (missing a polyp), pain, discomfort, bleeding (less than 1:300 cases), infection, distension, need to repeat the procedure, and infrequently but most seriously – the risk of perforation.  Perforation occurs when a small tear or hole occurs in the lining of the colon, which can require surgery to repair and rarely can lead to death.  These and other risks should always be discussed with your endoscopist prior to performing the procedure.  Get in touch with a medical specialist for free if you're interested in getting more information about colonoscopy.


Reviewed 12/12/2011 by David M. Nolan, M.D.
Diplomate of the American Board of Internal Medicine, 2011
Currently a Fellow of Gastroenterology, at UCI 2011-2014