What Is Flexible Sigmoidoscopy?

Medically Reviewed by Nayana Ambardekar, MD on September 14, 2022
3 min read


Flexible sigmoidoscopy is a test that a doctor uses to check the inner lining of your rectum and the lower part of your colon.

You may get this test if you have certain gut problems, such as abdominal pain, rectal bleeding, or changes in bowel habits. It’s also one of the tools that doctors use to check people for colon and rectal cancer.

A sigmoidoscope is a long, flexible tube that’s about half an inch in diameter. It has a tiny light and camera. A doctor uses it to view the lining of the rectum and the lower third of the colon.

First, tell your doctor if you:

  • Are pregnant
  • Have a lung or heart condition
  • Are allergic to any medications
  • Have diabetes or take drugs that may affect blood clotting

If you take certain medicines, your doctor may need to adjust them before you get this test.

Your bowel must be cleansed in order for sigmoidoscopy to be successful. Typically, a clear liquid diet the day before the test and overnight fasting are recommended. Your doctor will tell you how to do that and whether you need to adjust your diet before the test.

You will probably need at least one enema before the procedure, in order to empty out your rectum and lower intestine so that the test can show the intestinal walls.

Be sure to follow all of the prep instructions, so that the test can deliver the best results.

A flexible sigmoidoscopy usually lasts from 10 to 20 minutes. You may not need to be sedated.

Your doctor will have you lie on your left side, with your knees drawn up. They will insert the sigmoidoscope through the rectum and pass it into your sigmoid colon. The doctor will use a small amount of air to expand the colon to see the colon walls.

You may feel mild cramping during the procedure. To lessen those cramps, you can take several slow, deep breaths.

The doctor will slowly take the sigmoidoscope out while carefully examining the lining of your bowel.

After the procedure, your doctor will talk with you about the results.

If you weren't given a sedative for the procedure, you can go back to a normal diet and activities. 

If the doctor found any growths, or polyps, during the procedure, you may get a biopsy (removal of tissue) of the polyp or polyps. Or your doctor may recommend that you get a complete colon exam, by colonoscopy with polyp removal.

You may feel some cramping or feel like you're having gas, but this usually passes quickly.

It’s rare, but it’s possible that sigmoidoscopy could puncture the colon. If you have any of the following, call your doctor immediately:

  • Severe abdominal pain
  • Fever and chills
  • Heavy rectal bleeding (greater than 1 teaspoon at a time)