What is a Flexible Sigmoidoscopy?

Learn About Flexible Sigmoidoscopy and What to Expect With This Test

Mature male patient in discussion with doctor. Credit: Thomas Barwick / Getty Images

What is a Flexible Sigmoidoscopy?

A flexible sigmoidoscopy is a test that doctors use to look for and remove adenomas and polyps, growths in the colon that if left untreated, may turn into colon cancer. This test is also used to screen for colon cancer itself. Flexible sigmoidoscopy is one of the more common tests that can be used to screen for colon cancer. It doesn't require a specialist and can be performed by primary care doctors, clinical nurse specialists, nurse practitioners, and physician's assistants.

How Do You Prepare for a Flexible Sigmoidoscopy?

To prepare for this test, your doctor or nurse will give you instructions for the day or two before. This will involve taking laxatives or other medications and possibly following a special diet. This clears the stool out of your colon so your doctor can see everything clearly during the test.

You will be going to the bathroom a lot during the day before the procedure, so most people will take the day off of work or school to be close to the toilet at all times.

How Not to Dread Colon Cancer Screening provides detailed information on how to get ready for this test, along with tips for making this preparation easier.

Will I Be Sedated?

Most people don't need sedation for sigmoidoscopy. Discuss with your doctor what’s best for you. You can choose to be sedated during the procedure, but you’ll need a ride home if you go this route. You will not be allowed to drive or take public transportation.

You must be released to responsible adult who can ensure you get home safely after sedation, which also rules out taking a taxi.

What Happens During the Flexible Sigmoidoscopy Test?

The procedure is usually done in a private room. The procedure takes about 10 to 20 minutes. During a sigmoidoscopy, your doctor inserts a thin tube into your rectum and into the first two feet—or about half—of your colon.

Air will be put into your colon, as well, to allow for a better view. This may cause discomfort, but it should not hurt. If it does hurt, don’t suffer in silence; tell your doctor.

What Happens After My Flexible Sigmoidoscopy?

If your doctor finds any suspicious growths, often referred to as polyps or adenomas, he or she will remove them at that time. This colon tissue sample will be sent to a lab to check for cancer.

What are the Possible Complications of Flexible Sigmoidoscopy?

A possible complication of this test is puncture of the colon, but thankfully, this is very rare.

You may have some gas pains as the air from the test leaves your colon. You may also see a small amount blood in your stool for a day or two after the test, but this is usually not serious. If in doubt, call your doctor.

Another possible problem with this test is something called a false negative. What this means is that the test does not show colon cancer, when you actually do have the disease. Because the flexible sigmoidoscopy only allows the doctor to view a portion of your colon, it is possible that cancer in a part of your colon not seen on the test will be missed. A colonoscopy, which covers a larger portion of your colon, is less likely to give a false negative result.


Halpern MT, Pavluck AL, Ko CY, Ward EM. Factors Associated with Colon Cancer Stage at Diagnosis. Dig Dis Sci 2009 Jan 1. [Epub ahead of print].

Medline Plus. Colorectal Cancer. Accessed: 02/23/2016.

The American Cancer Society. Frequently Asked Questions About Colonoscopy and Sigmoidoscopy 02/02/2016.

The National Cancer Institute: Colon and Rectal Cancer. Accessed: 02/23/2016.

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