Frequently Asked Questions About Colonoscopy and Sigmoidoscopy

Colonoscopy (KO-lun-AH-skuh-pee) and sigmoidoscopy (SIG-moid-AH-skuh-pee) are screening tests used to look for colorectal cancer (commonly called colon cancer). They’re also used to look for polyps (PAH-lips) before they become cancer. (Polyps are growths on the lining of the colon.)

Learning more about these tests can help you decide which screening test is right for you. Here are some questions that you might have and answers for them:

What is colonoscopy?

Colonoscopy lets a doctor closely see the inside of the entire colon and rectum. The doctor is looking for polyps which could be an early sign of cancer. Polyps are small growths that over time can become cancer.

The doctor uses a thin (about the thickness of a finger), flexible, hollow, lighted tube that has a tiny video camera on the end. This tube is called a colonoscope (ko-LAHN-uh-SCOPE). The colonoscope is gently eased inside the colon and sends pictures to a TV screen. Small amounts of air are pumped into the colon to keep it open and let the doctor see clearly.

The exam itself takes about 30 minutes. You’ll probably be given medicine to help you relax and sleep while it’s done. You’ll need to plan on having someone go with you for this test so they can take you home afterwards.

Your health care provider decides how often you need this test, usually once every 10 years, unless you’re at a higher risk for colon cancer. It’s important that you talk with your provider to understand your risk for colon cancer, the guidelines you should follow for testing, and whether you need to start having the tests at age 50 or earlier.

What is sigmoidoscopy?

During sigmoidoscopy (SIG-moid-AH-skuh-pee), a doctor looks at part of the colon and the rectum. To do this, the doctor uses a thin (about the thickness of a finger), flexible, hollow, lighted tube called a sigmoidoscope (sig-MOID-uh-SCOPE) that has a tiny video camera on the end. Because the scope is only about 2 feet long, the doctor is able to see the entire rectum but less than half of the colon with this exam. The doctor is looking for signs of cancer or polyps. Polyps are small growths that can over time become cancer. The sigmoidoscope is gently eased inside the colon and sends pictures to a TV screen. Small amounts of air are pumped into the colon to keep it open and let the doctor see clearly.

The exam takes 10 to 20 minutes. Most people don’t need medicine to help them relax, but this may be an option that you can discuss with your healthcare provider ahead of time. Sedation may make the test less uncomfortable, but you’ll need time to recover from it and someone will have to take you home after the test.

Your health care provider decides how often you need this test, usually once every 5 years, depending on your colon cancer risk. It’s important for you to talk with your provider about your risk for colon cancer. This will help you know which guidelines you should follow for testing, and whether you need to start testing before age 50.

Will a colonoscopy or sigmoidoscopy hurt?

Most people don’t find these exams painful. Still, some people have more discomfort than others. You’re given medicine to make you sleep through a colonoscopy, so you don’t feel anything. Medicine usually isn’t used for a sigmoidoscopy.

During both of these tests, air is pumped into the cleaned-out colon to keep it open so that doctors can get the best pictures. The air pressure may cause some discomfort and cramping in your lower belly. You’ll feel better after the air leaves your colon.

As with most medical tests, complications are possible. Some can be serious – for instance, bleeding and puncture of the colon – but they’re rare. Make sure you understand how these tests work, how you can expect to feel during and after the test, and how to watch for possible problems that could come up afterward.

Who will do the exam?

Colonoscopy is almost always done by a doctor, usually a gastroenterologist (a doctor whose specialty is the digestive tract) or a surgeon.

Sigmoidoscopy exams are often done by primary care doctors (general practitioners, family doctors, and internal medicine doctors) in their offices. Clinical nurse specialists, nurse practitioners, or physician’s assistants can do sigmoidoscopies too.

Will I be in a private room?

Colonoscopy is done in a private area; it may be a hospital outpatient department, a clinic, an ambulatory surgery center, or a doctor’s office. Privacy is very important. If you have concerns, talk with the doctor about where and how the test will be done.

Sigmoidoscopy is most often done in a private room, with no other patients nearby. Doctors and nurses are very careful to respect patient privacy.

How do I get ready for a colonoscopy or sigmoidoscopy?

Many people consider the bowel preparation (often called the bowel prep) the worst part of these tests. For the doctor to see your insides clearly and get good pictures, your colon needs to be as cleaned out as possible.

You might be told to avoid certain foods and medicines and might be put on a clear liquid diet for a day or so before these tests. You’ll take very strong laxatives and might also need enemas to clean out your colon. If you can choose a day for your exam, pick one that will make it easy for you to be at home the day or evening before the test, when you do the bowel prep.

You’ll get instructions from your provider’s office ahead of time. Read them carefully since you may need to buy certain supplies (maybe clear liquids, like soups and gelatin) and get laxatives or enemas. If any of the instructions are not clear or you don’t understand them, call the office and go over them step-by-step. Also be sure to talk about any concerns you might have about the bowel prep.

Preparing for colonoscopy or sigmoidoscopy makes you to go the bathroom a lot! As soon as you take the laxatives, you’ll need to stay close to a bathroom. They usually start working pretty quickly  and your stool may become liquid. They might still be working the next morning when you go for your colonoscopy appointment. Don’t be embarrassed to ask for a bathroom when you get there. People have to ask this all the time and the staff is used to it.

How will I feel afterward? Will I need someone to drive me home? Will I need to miss work?

Most people feel OK after a colonoscopy. You could feel a bit woozy from the drugs. You’ll be watched as you wake up. You might have some gas because of the air that was pumped into the bowel, which can cause cramping and discomfort. Because of the medicines given for the test, you will need someone to take you home. Because colonoscopy is usually done with drugs that make you sleepy, most people miss work the day of the test.

After a sigmoidoscopy, you get up and walk out. There should be no problem driving yourself home, as long as you haven’t had any drugs to make you sleepy during the test. Ask your provider if you’ll need to miss work for a sigmoidoscopy.

What if they find something?

If a small polyp is found, the doctor will probably remove it during the test. Over time, some polyps could become cancer. If the doctor sees a large polyp, a tumor, or anything else abnormal, a biopsy (BY-op-see) will be done. For the biopsy, part or all of the polyp or abnormal area is taken out through the colonoscope or sigmoidoscope. It’s sent to a lab where it’s checked for cancer or pre-cancer cells.

If a polyp or colorectal cancer is found during sigmoidoscopy, you’ll need to have a colonoscopy later to check for polyps or cancer in the rest of your colon.

Why are these tests so important?

Colorectal cancer screening helps people stay well and saves lives. Regular colorectal cancer testing is one of the most successful ways to prevent colorectal cancer or find it early, when it’s small and easier to treat.

Removing polyps can help prevent colorectal cancer from ever starting. And cancers found in an early stage, while they are small and before they have spread, are easier to treat. Most people whose colon cancer is found and treated early will be alive 5 years later. And many will live a normal life span.

But all too often people don’t get any of these screening tests. Then the cancer can grow and spread without being noticed. Early on, colorectal cancer doesn’t usually cause any noticeable symptoms. In most cases, by the time people do have symptoms the cancer is advanced and very hard to treat.

Regular screening is the best way to find colon and rectal cancers in the early stages. Ask a health care provider about the best screening plan for you.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master's-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: February 2, 2016 Last Revised: February 2, 2016

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