Definition and Overview

Sigmoidoscopy is a test that looks into the last section of the colon, which is composed of the rectum, sigmoid colon, and the anus. It uses a device called bowel scope, a long, narrow, and flexible tube with an attached camera that feeds real-time images to a monitor and light that illuminates the sections being checked.

Sigmoidoscopy is different from colonoscopy, although both are intended to investigate issues affecting the gastrointestinal tract. While colonoscopy checks the entire colon, sigmoidoscopy focuses on the sigmoid colon, which is the last section of the large intestine that is connected to the rectum.

The procedure is performed on an outpatient basis and requires some preparation. There will be some mild discomfort, pressure, and pain after the procedure, but they’re expected to go away over time.

Who Should Undergo and Expected Results

Sigmoidoscopy is performed for a number of reasons, including the following:

  • There are changes in the bowel movement – Regular bowel movement can differ for every person, but often, it is consistent. The procedure is recommended if a person experiences recurrent diarrhea, constipation, or alternate diarrhea and constipation so the cause can be determined.
  • Stool has blood and/or mucus– Blood and mucus in the stool can indicate infection, perforation of the sigmoid colon, hemorrhoid, [anal fissure] when only a small amount of food has been consumed. Other symptoms include loss of appetite, malnutrition, and unexplained weight loss.
    Sigmoidoscopy can also be a part of a colon cancer screening. The US Preventive Services Task Force (UPSTF) recommends screening for colon cancer at age 50 or earlier if there’s a genetic or hereditary risk. Sigmoidoscopy is then performed every five years.

Sigmoidoscopy can reveal any perforation, ulceration, or growth of polyps in the colon, as well as tearing or bleeding in the rectum and anus.

How Does the Procedure Work?

Sigmoidoscopy can be performed by a general physician, an internist, or a gastroenterologist. Before the exam, the doctor will advise the patient to avoid taking medications, such as blood thinners, that can promote bleeding.

A significant part of the procedure is the bowel preparation, which involves getting rid of the stool in the colon. The doctor typically recommends a special diet like soups, broth, and tea. At least an hour before the procedure, the patient also undergoes an enema.

The procedure is often done on an outpatient basis either in a clinic or a hospital. Sedatives can be used to help the patient relax especially if the patient is a child so unnecessary movements can be minimised during the procedure.

The patient then lies on his side with his knees brought to the chest (foetal position). The doctor will begin by performing a digital rectal exam to check for any physical abnormality in the anus and rectum.

He will then proceed checking the sigmoid colon by gently and slowly inserting the bowel scope into the anus and rectum. As the probe enters, air is also introduced to further expand the colon. The camera provides the doctor with real-time images on a computer monitor helping him assess the affected organs.

Depending on what he sees, the doctor may remove a polyp for biopsy, obtain other samples for culture testing, determine if there’s any infection, or trace the source or cause of the inflammation, abscess, or ulceration. If there’s a polyp present, a colonoscopy will be most likely to be performed as well.

Once the procedure is complete, the doctor will slowly remove the bowel scope from the colon and anus. It usually takes around 20 minutes to complete the test.

Possible Risks and Complications

  • Passing stool or gas when air is introduced
  • Perforation or tearing of the colon
  • Bleeding
  • Infection
  • Discomfort and pressure during the digital rectal exam
  • Dizziness or nausea after the exam
  • Abdominal cramps
  • Bloating


  • Lieberman DA, Rex DK, Winawer SJ, Giardiello FM, Johnson DA, Levin TR; United States Multi-Society Task Force on Colorectal Cancer. Guidelines for colonoscopy surveillance after screening and polypectomy: a consensus update by the US Multi-Society Task Force on Colorectal Cancer.

  • Gastroenterology. 2012;143:844-57. PMID: 227613141

  • Pasricha PJ. Gastrointestinal endoscopy. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 134.

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