Screening for Colorectal Cancer:
Sigmoidoscopy and Colonoscopy

Colorectal cancer (CRC) screening can save lives by detecting and removing pre-cancerous lesions and polyps. Current CRC screening guidelines for the general public begin at age 50 and are summarized in Box 1. More frequent CRC screening may be necessary if you have a personal history of polyps or cancer. Check with your physician to determine the screening exams and schedules most appropriate for your personal medical or family history.

What is sigmoidoscopy and colonoscopy?

Two tests are available to assist the endoscopist (a physician specialist) in thoroughly examining the colon (large intestine) and rectum: sigmoidoscopy and colonoscopy. Sigmoidoscopy examines the left side of the colon with a sigmoidoscope. Colonoscopy examines the entire colon with a colonoscope. Both instruments have a very small video camera mounted in them to enable a physician to directly view the inside of the colon. For the test, a lighted, flexible tube about the thickness of an index finger is inserted through the rectum and into the large intestine. The colonoscope is longer than the sigmoidoscope.

During the procedure, a very small piece of tissue or a polyp can be removed from the large intestine [called a biopsy]. Biopsies are taken for many reasons and do not necessarily signal cancer. Polyps are removed because they can bleed, block the passage of stool, or become cancerous. The biopsy or polyp is then sent to a laboratory for examination. There is no pain when a biopsy or polyp is taken.

If a polyp is found during sigmoidoscopy of the left side of the colon, a colonoscopy at a later date will be necessary to examine the entire large colon.

How To Prepare for These Tests

The colon must be as clean as possible for the doctor to see any polyps or lesions during colonoscopy or sigmoidoscopy. Special directions for cleaning out the colon include the use of laxatives, enemas, and certain temporary dietary limitations, which your doctor or nurse will prescribe. Be sure to ask about any unusual side effects to watch for and report. Except under special circumstances, it is routine to be asked not to eat or drink anything after midnight before the examination. If you take regular medications, talk to your doctor about whether you can take them the day of the test or should temporarily stop them. Certain medications, such as aspirin and aspirin products can increase the risk of bleeding. It is helpful to bring a list of your medications and allergies with you the day of the test.

What To Expect When You Arrive

You may be asked to arrive at the hospital or clinic at least one half hour before a sigmoidoscopy and an hour before a colonoscopy. If you are receiving sedation (medicine to help you relax and rest during the procedure), you will need someone to drive or accompany you home since sedation can impair your judgment and reflexes.

You will change into a hospital gown, be assisted onto an exam table and a nurse will ask you some brief medical history questions. Your blood pressure and pulse will be measured. If you are receiving sedation, an IV with medicine will be inserted into one of your veins.

What Happens During the Procedure

You will be asked to lie on your left side. If you are having a sigmoidoscopy, the procedure will begin immediately. If you are having a colonoscopy, the nurse will place some devices on you to monitor how you are doing during your screening: 1) a blood pressure cuff on your arm to measure your blood pressure, 2) EKG leads (patches with wires placed on your chest) to record your heart rhythm, 3) a clip on your finger to record the oxygen in your blood, and 4) a tube placed under your nose to give you oxygen. When you are in "twilight sleep" (a light sleep) from the sedation, the colonoscopy is ready to begin.

For both the colonoscopy and sigmoidoscopy, the physician will first perform a rectal exam, and then place the scope into the rectum. Air is slowly introduced into your colon through the scope so the endoscopist can see the colon better. You may feel mild discomfort similar to cramps during the procedure. The endoscopist can suction air out through the scope or you can pass it to help relieve any cramps. If you are getting sedation, you may also get more medication.

After the procedure, you can leave immediately if you have not received sedation. If you have received sedation, you will go to the recovery room until you meet certain alertness criteria, and then you will be discharged with special instructions and in the care of the person who has accompanied you.

Some Possible Complications

Sigmoidoscopy and colonoscopy are generally safe, simple, and routine procedures with a low chance for complications. In very rare circumstances, a tear in the lining of the colon may occur requiring surgery. If a biopsy was taken or a polyp removed, traces of blood in the stool may be seen. In rare instances, a blood transfusion or surgery may be needed. There is also the chance of a reaction to the sedation medication. However, before you have either of these tests, all risks will be explained to you and you will be asked to sign a consent form.

Be An Informed Decision Maker

The decision to have a colonoscopy or a sigmoidoscopy will depend on a number of factors including age, personal medical history and family history of cancer. To take an active part in preventing colorectal cancer, talk with your doctor about which test is best for you and why.

Linda Hylind, BS, RN, is a colon cancer research nurse at The Johns Hopkins Hospital and The Johns Hopkins Hereditary Colorectal Cancer Registry.