What Is Sigmoidoscopy?

A sigmoidoscopy is a way for a doctor to examine the last one-third of the large intestine. This includes the rectum and sigmoid colon.

During the test, a flexible viewing tube with a lens and light source on the end, called a sigmoidoscope, is inserted through the anus and into the rectum. Then, looking through the eyepiece at the other end of the scope, the doctor can see the inside of the colon.

The test's purpose is to check for cancer, abnormal growths (polyps), and ulcers. Most of the time, a sigmoidoscopy is done by a gastroenterologist or a colorectal surgeon.

The test can be uncomfortable because there is no sedation, but most physicians keep the test very quick to cut down on patient discomfort. If there is prep and sedation, the test might take longer.

This article explains when the procedure is used, how it's done, the risks, and what to know about test results.

Purpose

Flexible sigmoidoscopy is a screening test. It is used to identify abnormalities in the lower colon and rectum. However, in the U.S., it is not widely used as a screening tool for colorectal cancer.

Your doctor may recommend the procedure if you are experiencing:

• Abdominal pain
• Rectal bleeding
• Chronic diarrhea
• Unusual bowel habits
  
• Other intestinal troubles

Even so, sigmoidoscopy has some advantages, including:

• It's a faster procedure
• Requires less prep time
• It does not require anesthesia

A sigmoidoscopy may also be used as a follow-up procedure if a digital rectal exam is abnormal or after a positive fecal occult blood test. It can also help identify the source of rectal bleeding or other problems in the lower digestive tract.

If your doctor finds something unusual during the procedure, they may be able to do a biopsy. For example, if an abnormality is found in a sigmoidoscopy, your doctor will probably want to follow up with a colonoscopy.

Some people at a higher risk for colorectal cancer may need to begin screening earlier. High-risk groups include those with:

• Inflammatory bowel disease (such as Chron's disease or ulcerative colitis)
• A family history of colorectal cancer or polyps
• A genetic syndrome like familial adenomatous polyposis (FAP) or hereditary Lynch syndrome
  

Risks

Like all medical procedures, sigmoidoscopy comes with certain risks. These include:

• Bleeding
• Perforation to the colon (a puncture in the organ)
• Abdominal pain
• Death (rare)

Bleeding and damage to the colon are the most common complications of sigmoidoscopy. Bleeding may occur up to two weeks following the procedure.

Before the Test

For the doctor to get a clear view of the intestinal wall, the colon must be empty. The doctor will give you specific instructions on how to prepare for the test. Preparation usually includes:

• Bowel prep that uses laxatives or enemas
• Diet consisting mainly of liquids (for example, broth, gelatin, plain coffee or tea, light-colored sports drinks and fruit juices, and water)

During the Test

A sigmoidoscopy is usually performed at a hospital or outpatient surgical center. The procedure usually takes about 20 minutes.

On the day of the test:

• Gown: You may be asked to wear a hospital gown or remove your clothes from the waist down.
• Vitals: A nurse or medical assistant may record temperature, pulse, blood pressure, and respiratory rate.
• Position: Your doctor will instruct you to lie on your left side on the exam table, with one or both knees raised to your chest.
• Scope insertion: Your doctor will insert the sigmoidoscope into your rectum. They may pump air through the scope if necessary for a clearer view.
• Image: The camera on the scope will send an image for your doctor to view.
• Biopsy: During the procedure, your doctor may perform a biopsy if they see something suspicious. They will do this using a device at the end of the sigmoidoscope. The tissue they collect can then be sent to a lab for further analysis under a microscope.
  

After the Test

After the procedure, you may resume normal activities, including eating and drinking. If you did not receive anesthesia, you could even drive yourself home.

Some people experience some discomfort after a sigmoidoscopy, including abdominal cramping or bloating. Also, if you had a biopsy, you might experience some bleeding from the anus.

If a biopsy is taken, your doctor should have the results in a few days.

Interpreting Results

Some results are available immediately after the procedure. Your doctor may share them with you before you leave.

If your doctor also performed a biopsy as part of the test, those results may take a few days or longer to come back.

If the test or biopsy results are positive or inconclusive, your doctor will likely recommend a colonoscopy. This test can look more closely at the entire colon.

Summary

Sigmoidoscopy is one of several screening options for colorectal cancer. Screening for this type of cancer is recommended for adults ages 45-75. If you choose sigmoidoscopy for cancer screening, it should be repeated every five years.

A sigmoidoscopy is limited to screening only the lower one-third of the bowel. This test is usually done without anesthesia in an outpatient surgical center or at a hospital. A colonoscopy is necessary to screen for cancer or polyps higher in the bowel.

A Word From Verywell

If you consider sigmoidoscopy for colorectal cancer screening, you should know that it is a little easier than a colonoscopy, but it is not as thorough. That's because it can only see part of the colon. Therefore, your doctor may determine that you need a colonoscopy after this test if they cannot see enough or find something concerning.

Discuss the different colorectal cancer screening tools with your doctor. Together, you can determine which timing and tools are best for you.