In sigmoidoscopy, a flexible, lighted viewing tube (sigmoidoscope) is passed into the anus, rectum, and the lowest portion of the large intestine, or sigmoid colon. Less often, a rigid scope is used, usually to examine just the anus or rectum. Fiberoptic cables permit the doctor to visually inspect the lining of these organs for any signs of disease or abnormality; in some cases, instruments are passed through the scope to obtain tissue biopsies or stool samples for microscopic examination. Sigmoidoscopy may also be done therapeutically, for example, to remove polyps.

Purpose of the Sigmoidoscopy

  • To detect and evaluate inflammatory or infectious bowel disease, hemorrhoids, polyps, tumors, ulcers, and other bowel abnormalities in people with symptoms such as blood or mucus in the stool, recent changes in bowel habits, or abdominal pain
  • Performed routinely—for example, every 3 to 5 years—to screen for colorectal cancer or precancerous polyps in adults age 50 and older; may be done earlier and more often in those with a family history of the disease or a positive fecal occult blood test.
  • To remove hemorrhoids or polyps, or reduce twisting (volvulus) in the lower bowel
  • To evaluate what is causing diarrhea, bleeding, colitis, changes in bowel habits, changes in stool and other symptoms.
  • To screen patients with a family history of colorectal cancer.
  • To detect inflamed tissue, abnormal growths and ulcers
  • To look for early signs of cancer
  • To help determine what may be causing otherwise unexplained changes in weight (loss) or bowel movements, abdominal pain or anal bleeding.

Who Performs It

  • A gastroenterologist or another physician

Special Concerns

  • Although sigmoidoscopy may provoke some anxiety, the procedure usually causes only mild to moderate discomfort.
  • You should wait at least a week after having a barium test, such as a barium enema, before undergoing sigmoidoscopy; the presence of barium interferes with visual inspection of the colon.
  • The procedure may not be possible in people with painful anorectal conditions, such as fissures or hemorrhoids, diverticulitis (inflammation in the sacs of the colon), or very active bleeding in the bowel or rectum.

Before the Sigmoidoscopy

  • Consume only clear liquids (for example, water, fat-free bouillon, strained fruit juice, plain coffee, plain tea, sports drinks, such as Gatorade or gelatin) for 12 to 48 hours before the procedure, according to your doctor’s instructions. You may have to fast on the morning of the procedure. In addition, some patients may also be prescribed an oral cathartic such as magnesium citrate.
  • The morning of the procedure, you may need to self-administer a cleansing enema before leaving your home, or you may be given an enema at the testing facility. This preparation will provide the examiner with a better view during the test.
  • If you are very anxious, you may receive a sedative injection, but this is not usually required.
  • If you have an anal fissure or local inflammation, you may be given a local anesthetic jelly shortly before the procedure.

What You Experience

  • You lie on your side on a table, with your knees drawn to your chest, and you are draped to minimize any embarrassment.
  • The doctor begins by inserting a gloved, lubricated finger into your rectum to perform a manual examination.
  • Next, the lubricated scope is gently inserted into your anus and through your rectum and the lower portion (up to 25 inches) of your colon. You may feel some abdominal cramping or the urge to defecate as the instrument is inserted and advanced. Breathe deeply and slowly through your mouth to relax your abdominal muscles and reduce this discomfort.
  • The doctor may instill a small amount of air through the scope to dilate the intestinal passage for better viewing. This may cause you to feel bloated and to pass gas.
  • As the scope is slowly withdrawn, the doctor carefully inspects the lining of your colon, rectum, and anus, looking for any abnormalities.
  • If appropriate, a biopsy forceps or other instrument may be inserted through the scope to obtain tissue or stool specimens. Polyps may be entirely removed using an electrocautery device. (These procedures are painless, since the colon lining contains no pain fibers; however, if a biopsy of the anal canal is needed, a local anesthetic is given since this area is sensitive to pain.) Tissue and fluid samples will be sent to a laboratory for analysis.
  • The procedure lasts 10 to 20 minutes.

Risks and Complications

  • When performed by a skilled professional, flexible sigmoidoscopy is typically safe and well-tolerated.
  • Possible complications include pain in the lower bowels, bleeding, infection, and, rarely, perforation of the rectum or colon (which requires surgical repair).

After the Sigmoidoscopy

  • You may leave the facility promptly after the test is completed. (Patients who have been given a sedative may need to wait until the medication wears off, and arrange for someone to drive them home.)
  • You may experience flatulence or gas pains after the procedure.
  • If a biopsy was performed, you may have a small amount of rectal bleeding for several hours.
  • Contact your doctor immediately if you develop fever, rectal bleeding, or abdominal pain and distention.


  • During visual inspection of the bowel, the doctor will note any abnormalities such as bleeding, inflammation, abnormal growths, or ulcers.
  • Various laboratory tests are often necessary to pinpoint a diagnosis. For example, stool samples may be cultured to identify the presence of infectious organisms. Biopsied tumors and excised polyps are examined under a microscope for signs of cancer or another abnormality.
  • If precancerous polyps or a malignancy are detected, you should undergo a more extensive procedure, called colonoscopy, to examine the entire length of the colon


The Johns Hopkins Consumer Guide to Medical Tests

Simeon Margolis, M.D., Ph.D., Medical Editor

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at

Published: 23 Jan 2012

Last Modified: 11 Sep 2015