In order for the doctor to perform a successful colonoscopy, the colon and rectum must be completely empty. Your doctor will give you complete instructions for how to prepare during the days preceding the tests, and specific foods and liquids to avoid eating and drinking. The day before the test you will be given laxative solution to clean out the colon. Many people find this cleansing more unpleasant than the colonoscopy itself.
Colonoscopy is generally a safe procedure. In very rare cases, complications such as bowel perforation can occur.
Flexible Sigmoidoscopy. Sigmoidoscopy is similar to colonoscopy but only examines the rectum and the lower two feet of the colon. (In contrast, colonoscopy allows the doctor to view the entire colon.) The procedure takes about 10 - 20 minutes, and sedation is optional. Preparation procedures are less demanding than those for colonoscopy.
Double-Contrast Barium Enema (DCBE). The double-contrast barium enema test uses an x-ray to image the entire large intestine. The test takes about 30 - 45 minutes, and sedation is not required. Preparations are similar to those for colonoscopy and sigmoidoscopy. For the test, barium sulfate is inserted into the rectum using a small, flexible tube. The colon is then pumped with air to help the barium spread through the colon. If polyps are detected in the x-ray, your doctor may recommend you have a colonoscopy for further investigation and removal.
Virtual Colonoscopy. Virtual colonoscopy, also called CT colonoscopy, uses x-rays delivered by computed tomography (CT) scan to take three-dimensional images of the colon. The test takes only 10 minutes to perform, and does not require sedation. (It does require the same preparations as standard colonoscopy to clean out the colon and bowel.) Air is pumped into the rectum through a small flexible tube. The patient is then slid into a CT scanner, which takes rapid images. Some recent studies indicate that CT colonoscopy has a high accuracy rate in detecting adenomas and cancers.
Fecal Occult Blood Test (FOBT). A fecal occult blood test is a take-home test that uses stool samples to detect hidden (occult) blood in feces. It may detect small amounts of blood in your stool from polyps or a tumor, even when your stools appear normal. Your doctor will give you a kit with instructions on how to take stool samples and prepare them for the kit. Your doctor will also inform you about what medications and foods need to be avoided in the days prior to the test. The test kit and samples are sent to a laboratory and results usually come back in a short time. If blood is found in the stool samples, you will need to have a colonoscopy.
Fecal Immunochemical Test (FIT). The fecal immunochemical test is a newer type of take-home test for hidden (occult) blood. The test is similar to the fecal occult blood test, but patients do not need to follow medication or dietary restrictions. As with the FOBT, a colonoscopy is recommended if blood is found in the stool.
Stool DNA Test. Like the FIT and the FOBT, the stool DNA test is conducted at home and uses fecal samples. Instead of testing for the presence of blood, this test looks for abnormalities in genetic material that come from cancer or polyp cells. These genetic changes are found in genes such as APC, K-ras, and p53. If DNA mutations are found, a colonoscopy is needed. The stool DNA test is new and not yet widely available. Some insurance carriers may not cover its cost.
Review Date: 10/21/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.