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A sigmoidoscopy ("flexible sigmoidoscopy") is a diagnostic test used to look for polyps and other changes in the intestine and to help detect colorectal cancer.

For information about each of the following aspects of a sigmoidoscopy in which you are interested, please click on the link.

Sigmoidoscopies are usually recommended every 5 years.

  • It is advisable to keep to the suggested schedule. If colorectal cancer occurs, the earlier it is detected, the more likely a person will survive.
  • To help you remember the schedule, ask the person close to you who is good at such things to help you keep track. (You can also set an alert in your computer).

NOTE: For information about other diagnostic techniques used to detect colorectal cancer, click here.

The Sigmoidoscopy Preparation And Procedure

Preparation for a Sigmoidoscopy

In order to obtain accurate results, the rectum and the lower colon must be completely clean of stool. Your doctor will give you detailed instructions on how to cleanse your colon. In general, this requires the use of one or two enemas prior to the procedure and may also call for a laxative and some dietary modifications. Under special circumstances, such as the presence of significant diarrhea, the preparation may be waived..

The Sigmoidoscopy Procedure

During a Sigmoidoscopy, a thin flexible lighted tube about two feet long (a sigmoidoscope) that the doctor can see through is carefully inserted into the anus. 

  • The sigmoidoscope goes up into the sigmoid colon (the rectum and the lower part of the colon). 
  • The tube may also have a tool to remove polyps or tissue samples, which are checked under a microscope for signs of cancer.
  • Air is blown gently into the intestinal tract so the doctor can see the intestinal lining more clearly.

The following image of a sigmoidoscopy is courtesy of the National Cancer Institute:


Sigmoidoscopy; shows sigmoidoscope inserted through the anus and rectum and into the sigmoid colon.  Inset shows patient on table having a sigmoidoscopy. offsite link

  • A sigmoidoscopy may be uncomfortable when air is blown into the intestinal tract because sedation is usually not used for the procedure.
  • You may feel cramping during the procedure and be bloated afterwards until the air is expelled. .For information about what happens during the procedure and recovery, click here.

If polyps are present: 

  • They can be removed through a sigmoidoscope. Samples can be biopsied for study by a pathologist.
  • A colonoscopy is usually needed to find out if there are additional polyps or cancer further in the colon. To learn about a colonoscopy, click here.

Advantages And Disadvantages Of A Sigmoidoscopy

Advantages of a sigmoidoscopy: 

  • The test is usually quick, with few complications.
  • Usually does not require sedation.
  • Many primary care doctors can do the test in their office.
  • Less extensive cleansing of the colon is necessary than for a colonoscopy.
  • For most patients, discomfort is minimal.
  • Can identify and remove polyps before they turn into cancer.
  • In some cases, the doctor may be able to perform a biopsy (the removal of tissue for examination under a microscope by a pathologist) and, if necessary, remove polyps during the test.
  • Moderate cost, covered by most health insurance.
  • Can accurately find polyps in the lower part of the colon (where most polyps occur).
  • If the results are normal, a more expensive colonoscopy will not be recommended.

Disadvantages of sigmoidoscopy: 

  • This test allows the doctor to view only the rectum and the lower part of the colon. Any polyps in the upper part of the colon will be missed.
  • May require enema preparation.
  • Patients may find the test uncomfortable and embarrassing.
  • There is a small risk of bleeding or tearing of the lining of the colon.
  • Additional procedures, such as a colonoscopy, may be necessary if the test indicates an abnormality.

How To Prepare For A Sigmoidoscopy

To prepare for a flexible sigmoidoscopy, one or more enemas are performed about 2 hours before the procedure to remove all solids from the sigmoid colon. An enema is performed by flushing water, laxative, or sometimes a mild soap solution into the anus using a special wash bottle. 

In some cases, the entire gastrointestinal tract must be emptied by following a clear liquid diet for 1 to 3 days before the procedure—similar to the preparation for colonoscopy. Patients should not drink beverages containing red or purple dye. For information about what is, and what is not, a clear liquid diet, click here

A laxative or an enema may also be required the night before a flexible sigmoidoscopy. A laxative is medicine that loosens stool and increases bowel movements. Laxatives are usually swallowed in pill form or as a powder dissolved in water.

Patients should inform their doctor of all medical conditions and any medications, vitamins, or supplements taken regularly, including:

  • Aspirin
  • Arthritis medications
  • Blood thinners
  • Diabetes medications
  • Vitamins that contain iron

What To Expect During And After A Sigmoidoscopy

Examination of the Sigmoid Colon

During a flexible sigmoidoscopy, patients lie on their left side on an examination table.

The doctor inserts a long, flexible, lighted tube called a sigmoidoscope, or scope, into the anus and slowly guides it through the rectum and into the sigmoid colon. The scope inflates the colon with air to give the doctor a better view. A small camera mounted on the scope transmits a video image from inside the colon to a computer screen, allowing the doctor to carefully examine the tissues lining the sigmoid colon and rectum.

The doctor may ask the patient to move periodically so the scope can be adjusted for better viewing.

When the scope reaches the transverse colon, the scope is slowly withdrawn while the lining of the colon is carefully examined again.

Biopsy and Removal of Colon Polyps

The doctor can remove growths, called polyps, during a flexible sigmoidoscopy by using special tools which are passed through the scope. Polyps are common in adults and are usually harmless. However, most colon cancer begins as a polyp, so removing polyps early is an effective way to prevent cancer.

If bleeding occurs, the doctor can usually stop it with an electrical probe or special medications passed through the scope.

During a flexible sigmoidoscopy, the doctor can also take samples from abnormal-looking tissues. Called a biopsy, this procedure allows the doctor to later look at the tissue with a microscope for signs of disease.

Tissue removal and the treatments to stop bleeding are usually painless. If polyps or other abnormal tissues are found, the doctor may suggest examining the rest of the colon with a colonoscopy.

Drawing of the gastrointestinal tract with labels pointing to the ascending colon, transverse colon, sigmoid colon, rectum, and anus. The ascending colon and the sigmoid colon are shaded.

The sigmoid colon is the last one third of the colon.

A flexible sigmoidoscopy takes about 20 minutes.


Cramping or bloating may occur during the first hour after the procedure. Bleeding and puncture of the large intestine are possible but uncommon complications. Discharge instructions should be carefully read and followed.

To help get rid of the gas:

  • Walk if it is not too painful. 
  • Lay on your side like a baby in the womb (the fetal position).

The following side effects are rare. Patients who develop any of these side effects should contact their doctor immediately:

  • Severe abdominal pain
  • Fever
  • Bloody bowel movements
  • Dizziness
  • Weakness