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Frequently Asked Questions About Colonoscopy and Sigmoidoscopy

Colonoscopy (ko-lun-AH-skuh-pee) and sigmoidoscopy (sig-moid-AH-skuh-pee) are two screening exam options that may be used to look for colorectal cancer (commonly referred to as colon cancer). They’re also used to look for polyps (pah-lips) before they become cancer.

False information and a misplaced sense of modesty have scared many people away from these tests. Learning more about them can help you decide which screening test is right for you. Here are some questions you might have and some answers for them:

What is colonoscopy?

Colonoscopy (ko-lun-AH-skuh-pee) is an exam that lets a doctor closely look at the inside of the entire colon and rectum. The doctor is looking for polyps (pah-lips) or signs 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 puffed into the colon to keep it open and let the doctor see clearly.

The exam itself takes about 30 minutes. Patients are usually given medicine to help them relax and sleep while it’s done.

Your doctor decides how often you need this test, usually once every 10 years, depending on your estimated risk for colon cancer. It’s important for you to talk with your doctor 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 closely looks at only the lower 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 (pah-lips). Polyps are small growths which 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 puffed into the colon to keep it open and let the doctor see clearly.

The exam takes 10 to 20 minutes. The patient usually doesn’t need medicine to help them relax, but this might be an option you can talk about with your doctor.

Your doctor decides how often you need this test, usually once every 5 years, depending on your estimated risk for colon cancer. It’s important for you to talk with your doctor to understand your risk for colon cancer. You will want to be sure about the guidelines you should follow for testing, and whether you need to start having tests at age 50 or earlier.

Will it hurt?

Most people don’t find these exams painful, although some people have more discomfort than others. Patients are given medicine to make them sleep through a colonoscopy, so they 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.

As with most medical tests, complications are possible with both of these tests. Some can be serious – for instance, bleeding and puncture of the colon – but they’re very uncommon. 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 may 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. Studies show that a well-trained clinical nurse specialist, nurse practitioner, or physician’s assistant can do sigmoidoscopies very well 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. The patient’s privacy is very important. If you have concerns, talk with the doctor about where and how the procedure will be done.

Sigmoidoscopy typically is done in a private room, with no other patients nearby. Doctors and nurses are professional and very careful to respect the patient’s privacy.

How do I prepare? Will I need to miss work?

Preparing for colonoscopy or sigmoidoscopy makes you to go the bathroom a lot! Your doctor will give you instructions. Read them carefully a few days ahead of time, since you may need to shop for special supplies and get laxatives or enemas from a pharmacy. You usually start your preparation a day or 2 before the actual test, and you may need to change your plans for the preparation day. You’ll need to be near a bathroom as soon as you start the laxatives. If any of the instructions are not clear or you do not understand them, call the doctor’s office and go over them step by step with the nurse.

Many people consider the bowel preparation (often called the bowel prep) the worst part of these tests. You may need to follow a special diet for one or more days before these exams and take very strong laxatives before either procedure. You may also need enemas to clean out your colon. In order for the doctor to see the inside of your rectum and colon clearly and get good pictures, your bowels need to be as cleaned out as possible. For either test you’ll need to stay close to a bathroom the day before and the morning of the test.

Because colonoscopy is usually done with drugs that make you sleepy, most people miss work the day of the test. Ask your doctor if you’ll need to miss work for a sigmoidoscopy. You might want to schedule the test the day after a scheduled day off, so you can be at home the day before without taking an extra day off.

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

Most people feel OK after a colonoscopy. They may feel a bit woozy from the drugs (anesthesia). They’ll be watched as they wake up. They may 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.

After a sigmoidoscopy, you get up and walk out. There should be no problem driving yourself home, as long as you have not had any drugs to make you sleepy during the test.

What if they find something?

If a small polyp is found, your doctor will probably remove it during the test. Over time some polyps could become cancer. If your 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 for a doctor to look at under a microscope and check for cancer or pre-cancer cells.

If a polyp or colorectal cancer is found during sigmoidoscopy, you will 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 powerful weapons for preventing colorectal cancer or finding it early, when it’s easier to treat. There are 2 basic types of screening tests:

  • Tests that mainly find cancer: These involve testing the stool (feces) for signs that cancer may be present. These tests are easier, but they are also less likely to detect polyps.
  • Tests that can find both colorectal polyps and cancer: These tests look at the structure of the colon itself to find any abnormal areas. Colonoscopy and sigmoidoscopy fall in this group, along with double-contrast barium enema and CT colonography (virtual colonoscopy). These tests are preferred if they are available and you are willing to have them.

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 more easily treated. Nine out of 10 people whose colon cancer is discovered 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 changes that are noticed (symptoms). In most cases, by the time people do have symptoms the cancer is advanced and very hard to treat.

Regular screening is the most reliable way to find these cancers in the early stages. Ask a doctor about the best screening plan for you.


Last Medical Review: 06/12/2013
Last Revised: 06/12/2013