Medically reviewed on Oct 25, 2018
A flexible sigmoidoscopy (sig-moi-DOS-kuh-pee) is an exam used to evaluate the lower part of the large intestine (colon). During a flexible sigmoidoscopy exam, a thin, flexible tube (sigmoidoscope) is inserted into the rectum.
A tiny video camera at the tip of the tube allows the doctor to view the inside of the rectum and most of the sigmoid colon — about the last two feet (61 centimeters) of the large intestine. If necessary, tissue samples (biopsies) can be taken through the scope during a flexible sigmoidoscopy exam.
Flexible sigmoidoscopy doesn't allow the doctor to see the entire colon. As a result, any cancers or polyps farther into the colon can't be detected with flexible sigmoidoscopy alone.
During a flexible sigmoidoscopy exam, the doctor inserts a sigmoidoscope into your rectum to check for abnormalities in your lower colon.
Why it's done
Your doctor may recommend a flexible sigmoidoscopy exam to:
- Investigate intestinal signs and symptoms. A flexible sigmoidoscopy exam can help your doctor explore possible causes of abdominal pain, rectal bleeding, changes in bowel habits, chronic diarrhea and other intestinal problems.
Screen for colon cancer. If you're age 50 or older and you have no colon cancer risk factors other than age — which puts you at average risk — your doctor may recommend a flexible sigmoidoscopy exam every five years to screen for colon cancer.
Sigmoidoscopy is one option for colon cancer screening, but there are other options that allow visualization of the whole colon. Talk with your doctor about your options.
- Sigmoidoscopy may occasionally be preferred over colonoscopy because the preparation for sigmoidoscopy and the test itself may take less time. In addition, anesthetic is often not required. There is a lower risk of direct harm such as perforation with sigmoidoscopy compared with colonoscopy.
A flexible sigmoidoscopy exam poses few risks. Rarely, complications of a flexible sigmoidoscopy exam may include:
- Bleeding from the site where a tissue sample (biopsy) was taken
- A tear in the colon or rectum wall
How you prepare
Before a flexible sigmoidoscopy exam, you'll need to clean out (empty) your colon. Any residue in your colon may obscure the view of your colon and rectum during the exam.
To empty your colon, follow your doctor's instructions carefully. You may be asked to:
- Follow a special diet the day before the exam. Typically, you won't be able to eat the day before the exam. Drinks may be limited to clear liquids — plain water, broth, carbonated beverages, and tea and coffee without milk or cream. You may be asked not to eat or drink anything after midnight the night before the exam.
- Take a laxative the night before the exam. The laxative will be in either pill or liquid form.
- Use an enema kit. In some cases, you may need to use an over-the-counter enema kit — either the night before the exam or a few hours before the exam — to empty your colon. Or you may be asked to take two enemas at home the morning of the procedure.
- Adjust your medications. Remind your doctor of your medications at least a week before the exam — especially if you have diabetes, if you take medications or supplements that contain iron, or if you take aspirin or other blood thinners. You may need to adjust your dosages or stop taking the medication temporarily.
What you can expect
During the exam
Wearing a gown, you'll begin the exam lying on your side on the exam table, usually with your knees drawn toward your chest. The doctor will insert a sigmoidoscope into your rectum.
The sigmoidoscope contains a light and a tube (channel) that allows the doctor to pump air into your colon. The air expands the colon, which provides a better view of the colon lining. When the scope is moved or air is introduced, you may feel abdominal cramping or the urge to move your bowels.
The sigmoidoscope also contains a tiny video camera at its tip. The camera sends images to an external monitor so that the doctor can study the inside of your colon. The doctor can also insert instruments through the scope to take tissue samples (biopsies).
A flexible sigmoidoscopy exam typically takes about 15 minutes. It may require slightly more time if biopsies are taken. Sedation and pain medications usually aren't necessary. If a polyp is found, your doctor will likely recommend a full colonoscopy to look at your whole colon, as other polyps may be present further up in the colon.
After the exam
After the exam, you may have mild abdominal discomfort. You may feel bloated or pass gas for a few hours as you clear the air from your colon. Walking may help relieve any discomfort. You should be able to return to your usual diet and activities right away.
You may also notice a small amount of blood with your first bowel movement after the exam, which usually isn't cause for alarm. Consult your doctor if you continue to pass blood or blood clots or if you have persistent abdominal pain or a fever of 100 F (37.8 C) or higher.
Your doctor will review the results of your flexible sigmoidoscopy exam and then share them with you.
- Negative result. The results of a flexible sigmoidoscopy exam are considered negative if the doctor doesn't find any abnormalities in the colon. If you're at average risk of colon cancer — you have no colon cancer risk factors other than age — your doctor may recommend waiting five years before repeating the exam.
- Positive result. The results of a flexible sigmoidoscopy exam are considered positive if the doctor finds polyps or abnormal tissue in the colon. Depending on the findings, you may need additional testing — such as a colonoscopy — so that any abnormalities can be examined more thoroughly, biopsied or removed. During colonoscopy, your doctor can also screen the entire colon for other abnormalities.
How much of your colon and rectum can be viewed during a flexible sigmoidoscopy depends on the experience of the doctor doing your exam, the anatomy of your colon and the success of the colon preparation. If your doctor is concerned about the quality of the view through the scope, he or she may recommend a repeat flexible sigmoidoscopy exam or another screening test.