Colon Exam

To help diagnose or rule out conditions like ulcerative colitis, Crohn disease, diverticulosis, and colorectal cancer, your gastroenterologist may need to perform a rectum and colon exam to view the inside of your colon and rectum. Three tests are available to obtain this inner view of the lower gastrointestinal tract: barium enema, sigmoidoscopy, and colonoscopy. All three procedures can be performed on an outpatient basis in a health clinic, a doctor’s office, or a day-surgery (outpatient) department associated with a hospital. For the most accurate results, follow your doctor’s specific instructions before the procedure.

Barium enema

For this type of colon exam, barium sulfate—a type of contrast dye—is infused through the anus and into the colon to produce x-ray images of the lower gastrointestina tract. Before undergoing a barium enema, the colon must be emptied. To accomplish this, you will be asked to consume a mainly liquid diet for about a day before the procedure. Water, fat-free broth or bouillon, Jell-O, black coffee, plain tea, diet soda, and fruit juice are appropriate for this diet. In addition, you should not eat or drink anything after midnight the night before the procedure. The process of cleansing the colon is often augmented with laxatives, which should be taken according to your doctor’s instructions. On the morning of the procedure, an enema is needed to cleanse the colon completely.

During a barium enema, you will lie on your side with your knees bent toward your chest. A lubricated tube is gently inserted through the anus into the rectum. Barium is then passed through the tube into the rectum, allowing the colon to fill with the contrast dye. You may feel some abdominal discomfort or an urge to pass stool during the test. A radiologist will take continuous x-rays of the abdomen and view them on a screen. If any abnormalities are seen, the radiologist will take spot x-rays for later analysis. When the procedure is complete (typically after 30 to 45 minutes), you will be taken to the bathroom so you can expel some of the barium into the toilet. Laxatives may assist in this process.

If a buildup of the barium prevents you from having a bowel movement in the days after the test, your doctor may recommend a laxative or an enema. Also, your stool may be a whitish color for up to three days after the procedure because of the barium. Serious complications, such as perforation of the colon, are extremely rare.


During a sigmoidoscopy, a doctor examines the inside of your rectum and sigmoid colon (the last part of the large intestine) using a two-foot long flexible viewing tube called a sigmoidoscope.

As with a barium enema, cleansing of the colon is necessary before a sigmoidoscopy. To achieve this, a mainly liquid diet is necessary for up to two days before the procedure. Roughly 20 hours prior to the sigmoidoscopy, you will also need to take a laxative. In addition, you are typically not allowed to eat on the morning of the exam or drink anything during the four hours prior to the test. An enema is required on the morning of the procedure.

Usually no sedation is required for a sigmoidoscopy. While you lie on your left side, the gastroenterologist manually inspects the anus and rectum for any blockages and then gently
inserts the sigmoidoscope into the rectum and the lower colon to view the inner lining of these structures. The physician may take biopsies and remove any abnormal growths that are seen. The sigmoid colon exam procedure takes up to 30 minutes, and, if no sedation was necessary, you usually can drive yourself home afterward. You may experience gas or a small amount of bleeding following a sigmoidoscopy. More serious complications, such as pain, excessive bleeding, and perforation of the colon or rectum, can occur but are extremely rare.


A colonoscopy is very similar to a sigmoidoscopy, except that a longer flexible viewing tube called a colonoscope is used to examine the entire colon and at times the lower portion of the small intestine.

Before a colonoscopy, you need to be on a mainly liquid diet for up to three days. The doctor will also prescribe a strong oral laxative to take on the evening prior to the test. You
should be sure to drink enough water to avoid dehydration while on the diet, but do not eat or drink anything after midnight on the night before the procedure.

Just before the colonoscopy, you will receive pain medication and a mild sedative intravenously. While you lie on the examining table, the doctor manually checks for blockages in the anus and rectum, then gently inserts the tube through the anus and rectum and into the colon. As the colonoscope is slowly withdrawn, the doctor inspects the lining of the intestine and may take biopsies of any abnormal tissue and remove any abnormal growths. You may experience abdominal cramping, bloating, and a need to pass stool or gas during the procedure. The whole process can take up to an hour.

You will need to wait about an hour after the procedure for the sedation to wear off. Someone else will have to drive you home because of the lingering effect of the sedative. It is common to have gas after the procedure and to have minor rectal bleeding if a biopsy was taken. Serious complications are rare (occurring in fewer than 0.1% of all colonoscopies) and can include excessive bleeding, labored breathing (as a result of the sedative), and perforation of the colon or rectum.