Approved by the Cancer.Net Editorial Board, 08/2018

A sigmoidoscopy is a way to view the lower 20 inches of a person's sigmoid colon and rectum. It is one way to screen for colorectal cancer or intestinal polyps. Polyps are small abnormal growths that may become cancerous. Sigmoidoscopy is also a diagnostic test for people who have rectal bleeding, a change in bowel habits, or other symptoms.

Finding polyps in the lower part of the colon means there is a higher chance of having them elsewhere in the colon. So, if your doctor finds polyps during your sigmoidoscopy, he or she will likely recommend a colonoscopy. A colonoscopy allows the doctor to look at the entire colon.

About the large intestine and colon

The sigmoid colon and rectum are part of the large intestine. The large intestine helps the body process waste. The first 5 to 6 feet of the large intestine is the colon. The last 6 inches of the large intestine is the rectum, ending at the anus.

The drawing below shows the different parts of the colon and rectum.

This illustration shows the 5 sections of the colon and rectum. The ascending colon is the beginning the large intestine into which the small intestine empties; it begins on the lower right side of the abdomen and then leads up to the transverse colon. The transverse colon crosses the top of the abdomen from right to left, leading to the descending colon, which takes waste down the left side. Finally, the sigmoid colon at the bottom takes waste a few more inches, down to the rectum. A cross-section of the rectum and sigmoid colon shows where waste leaves the body, through the anus. Copyright 2004 American Society of Clinical Oncology. Robert Morreale/Visual Explanations, LLC.

How a sigmoidoscopy works

A sigmoidoscopy is done with a device called a sigmoidoscope. A sigmoidoscope is a pencil-thin, flexible tube with a light and a camera on the end. During a sigmoidoscopy, the doctor inserts the sigmoidoscope into the anus, through the rectum, and into the lower part of the colon. The doctor views the inside of the colon through the scope or on a video monitor.

Who does my sigmoidoscopy?

A gastroenterologist or surgeon usually performs a sigmoidoscopy with the help of a nurse in a doctor's office or hospital. A gastroenterologist specializes in the gastrointestinal tract, including the stomach and intestines. A primary care or family practice doctor, nurse practitioner, or physician assistant may also perform the procedure.

Getting ready for a sigmoidoscopy

When you schedule the exam, your doctor will give you detailed instructions on how to prepare. Here are some general suggestions:

What to eat. You may need to follow a liquid diet for up to 24 hours before the exam. This means only eating foods such as fat-free bouillon or broth, black coffee, strained fruit juice, or gelatin.

Emptying your colon. Your lower colon must be empty for the doctor to examine it. So, you will need to use an enema or strong laxatives the night before or the day of the sigmoidoscopy. If your doctor prescribes a laxative, it will be either a pill or a powder that you mix with water before drinking. The laxative will make you use the bathroom frequently. Make sure you have easy access to a bathroom during this time.

Topics to discuss with your health care team. Be prepared to discuss the following topics with your health care team:

  • Medications you are taking. Ask whether you should take them on the day of the test. You may need to stop taking medications that increase your risk of bleeding for a few days before the sigmoidoscopy. These medications include aspirin and other blood thinners.

  • Any drug allergies or other health conditions

  • Any concerns you may have about the test

Insurance, cost, and consent. Before your appointment, find out from your insurance provider what costs will be covered. Ask how much of the cost you will have to pay. Once you arrive at the doctor's office or hospital, you will be asked to sign a consent form. This form states that you understand the benefits and risks of the procedure and that you agree to have it.

During the procedure

How long will it take? A sigmoidoscopy usually takes about 15 to 20 minutes to complete.

What should I wear? You will be given a hospital gown to wear.

What will happen during the procedure?

  • When you arrive for your sigmoidoscopy, you will need to remove your clothing and put on a hospital gown.

  • The doctor will ask you to lie on your side on an exam table and will drape a sheet over your body.

  • Then, the doctor will gently insert the lubricated scope into your rectum. He or she will use the scope to blow air into your colon. This inflates it and makes it easier to examine. You may feel bloated or like you need to go to the bathroom.

  • If the doctor finds a polyp in your colon during the exam, he or she will remove a piece of tissue or the entire polyp. The doctor does this using a tool attached to the end of the sigmoidoscope.

  • Your doctor will send the tissue sample to a laboratory where a pathologist will examine it under a microscope to find out if it is cancerous.

Is it painful? Generally, a sigmoidoscopy is uncomfortable but not painful. The doctor will probably perform it without anesthesia. But the doctor may give you sedatives if you are anxious about the procedure. If you start to feel pain at any time, tell the doctor so he or she can reposition the sigmoidoscope.

After the procedure

You can expect to return to normal activities, including driving, right after the sigmoidoscopy. If your doctor gave you a sedative, you will be groggy after the procedure. So, it is important to arrange ahead of time for a friend or family member to drive you home.

What should I expect after returning home? At first, you may feel cramps or bloating. But that discomfort usually passes quickly. People often release the gas that was put into the colon during the procedure. Some people may experience diarrhea while releasing the gas. Minor bleeding from the rectum may also occur. If you have abdominal pain, major bleeding, dizziness, weakness, or a fever, call your health care team.

Questions to ask the health care team

Before a sigmoidoscopy, consider asking your health care team these questions:

  • Who will perform the sigmoidoscopy? Will anyone else be in the room during the procedure?

  • How should I prepare for the procedure? Are there restrictions on what I may eat or drink the day before?

  • Can I take my regular medications the day of the test? Which ones should I not take and when can I take them again?

  • What will happen during the sigmoidoscopy?

  • How long will the procedure take?

  • Will it be painful?

  • What are the benefits and risks of having a sigmoidoscopy?

  • Will I be given sedatives or anesthesia?

  • Will I need to avoid any activities after the sigmoidoscopy?

  • Will I need to have someone drive me home from the procedure?

  • When will I learn the results?

  • When and how will I learn the results?

  • Who will explain the results to me?

  • Will I need other tests?

Related Resources

Types of Endoscopy

Cancer Screening

More Information

National Institute of Diabetes and Digestive and Kidney Diseases: Flexible Sigmoidoscopy

National Cancer Institute: Colorectal Cancer Screening