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Sigmoidoscopy is a procedure used to look at the colon and determine the cause of digestive problems. Learn how it's done.

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image of a scope Sigmoidoscopy

The sigmoid colon is the last portion of the colon where water is absorbed and stool is formed. Its muscular folds move food through the last stages of digestion.

The sigmoid colon can also be the site of diseases such as colon cancer and ulcerative colitis.

Experts advise that everyone from age 50 to 75 be screened for colon cancer using either sigmoidoscopy, colonoscopy or fecal occult blood testing.

What is sigmoidoscopy?
Sigmoidoscopy is a procedure in which a thin, flexible tube with a light source and eyepiece or video camera is passed through the lower part of the large intestine.

The doctor uses the scope to see the inside of the large intestine from the rectum through the last part of the colon (sigmoid). With this the doctor can find tumors, polyps - outgrowths from the surface - ulcers and other abnormalities.

Why would I need this test?
Sigmoidoscopy is a test used to find the cause of diarrhea, abdominal pain, blood in stool or constipation. It is also one of the screening tests for colon or rectal cancer.

How do I prepare for this test?
Your colon and rectum must be empty for the procedure to be thorough and safe. You will probably be instructed to drink only clear liquids for 12 to 24 hours beforehand. A liquid diet means fat-free bouillon or broth, gelatin, strained fruit juice, water, plain coffee or tea, or soda. The night before or right before the procedure, you may also need to take laxatives or have an enema to remove all stool from the intestines. You may also be told to avoid aspirin or certain other medicines for several days before the test. Your doctor will give you detailed instructions.

How is this test performed?
For the procedure, you will lie on an exam table, on your left side with your knees drawn up toward your chest.

A doctor inserts a thin tube through the rectum and slowly passes it up through the colon. A small amount of air is injected so the colon expands slightly. This gives the doctor a better view and helps guide the tube.

You may be asked to move during the exam so the doctor can adjust the scope for better viewing. The procedure takes about 20 minutes. During the procedure, you might feel pressure and slight cramping in your lower abdomen.

How is sigmoidoscopy used to screen for colorectal cancer?
Doctors are not able to see the entire colon with a sigmoidoscope. A polyp or other abnormal finding seen during this test would trigger your doctor to order further testing, such as a colonoscopy. A colonoscope is long enough to view the entire colon. Colonoscopy is the "gold standard" to find colon cancer, but it is more invasive and carries more risk.

Other screening methods are the fecal occult blood test and barium enema. The fecal occult blood test detects microscopic blood in the stool, which may be a sign of colon cancer. A barium enema uses contrast dye to visualize the entire colon with x-ray images. You may be offered a barium enema if doing a sigmoidoscopy or colonoscopy is too risky.

Screening for colon cancer begins at age 50. It may start earlier if you have risks for colon cancer, such as a family history. The type or combination of screening tests offered will take into account your personal and family history and other factors. One example of a screening schedule is a combination of a fecal occult blood test and sigmoidoscopy every five years. Discuss with your doctor what screening is best for you and how often you need screening.

What happens if an abnormality is found?
If anything unusual is seen in your rectum or sigmoid colon, such as a polyp or inflamed tissue, the doctor can remove a piece of it or all of it using small surgical instruments inserted through the scope. The tissue (biopsy) is sent to the lab for testing. Also, if abnormalities are found, your doctor may suggest a colonoscopy or other testing to examine the entire colon.

Are there any risks associated with this test?
Complications are uncommon, but bleeding and puncture of the colon are possible. You may have some cramping and bloating for about one hour after the procedure.

What is a desirable result?
A normal colon will appear light pink or orange, with half-moon shaped folds. The rectum and colon will be free from infection, hemorrhoids, tumors, polyps, ulcers or fissures (tears).

By Louis Neipris, MD, Staff Writer
Created on 08/01/2001
Updated on 11/11/2009
  • Guirguis-Blake J, Meyers D, Crichlow R, Wilson JE, Carter C. Preventive services by disease category. In: Rakel RE. Rakel: Textbook of Family Medicine. 7th ed. Philadelphia, PA: Saunders Elsevier; 2007.
  • Agency for Healthcare Research and Quality. U.S. Preventive Services Task Force. Screening for colorectal cancer. Recommendation statement.
  • National Cancer Institute. Colorectal cancer screening.
  • National Institute of Diabetes and Digestive and Kidney Diseases. Flexible sigmoidoscopy.
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