Colonoscopy

Test Overview

Colonoscopy is a test that allows your doctor to look at the inner lining of your large intestine (rectum and colon). He or she uses a thin, flexible tube called a colonoscope to look at the colon. A colonoscopy helps find ulcers, colon polyps, tumors, and areas of inflammation or bleeding. During a colonoscopy, tissue samples can be collected (biopsy) and abnormal growths can be taken out. Colonoscopy can also be used as a screening test to check for cancer or precancerous growths in the colon or rectum (polyps).

The colonoscope is a thin, flexible tube that ranges from 48 in. (122 cm) to 72 in. (183 cm) long. A small video camera is attached to the colonoscope so that your doctor can take pictures or video of the large intestine (colon). The colonoscope can be used to look at the whole colon and the lower part of the small intestine. A test called sigmoidoscopy shows only the rectum and the lower part of the colon.

Before this test, you will need to clean out your colon (colon prep). Colon prep takes 1 to 2 days, depending on which type of prep your doctor recommends. Some preps may be taken the evening before the test. For many people, the prep for a colonoscopy is more trying than the actual test. Plan to stay home during your prep time since you will need to use the bathroom often. The colon prep causes loose, frequent stools and diarrhea so that your colon will be empty for the test. The colon prep may be uncomfortable and you may feel hungry on the clear liquid diet. If you need to drink a special solution as part of your prep, be sure to have clear fruit juices or soft drinks to drink after the prep because the solution tastes salty.

For more information on screening tests for colon cancer, see:

Which test should I have to screen for colorectal cancer?

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Why It Is Done

Colonoscopy is done to:

• Check for colorectal cancer or polyps.
  • Screening tests are recommended by the American Gastroenterological Association, the American Cancer Society, and the U.S. Preventive Services Task Force (USPSTF). These groups advise people who have no risk factors to be tested starting at age 50.
  • The American Gastroenterological Association recommends that people with a family history of colon cancer have a colonoscopy at age 40, or 10 years before the age that the relative got cancer.
  • If you are at increased risk for colon cancer, talk to your doctor about which test is best for you and how often you should have the test.
• Check for the cause of blood in the stool or rectal bleeding.
• Check for the cause of dark or black stools.
• Check for the cause of chronic diarrhea.
• Check for the cause of iron deficiency anemia.
• Check for the cause of sudden, unexplained weight loss.
• Check the colon after abnormal results from a stool test or a barium enema test.
• Watch or treat inflammatory bowel disease (IBD).
• Check for the cause of long-term, unexplained belly pain.

How To Prepare

Before you have a colonoscopy, tell your doctor if you:

• Are taking any medicines, such as insulin or medicines for arthritis. Check with your doctor about which medicines you need to take on the day of your test.
• Are allergic to any medicines, including anesthetics.
• Have bleeding problems or take blood thinners, such as aspirin or warfarin (Coumadin)
• Had an X-ray test using barium, such as a barium enema, in the last 4 days.
• Are or might be pregnant.

You may be asked to stop taking aspirin products or iron supplements 7 to 14 days before the test. If you take blood-thinning medicines regularly, discuss with your doctor how to manage your medicine.

You will be asked to sign a consent form that says you understand the risks of colonoscopy and agree to have the test done. Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?) .

Before this test, you will need to clean out your colon. The following information gives you a general idea of the preparation for a colonoscopy. Your doctor will give you specific instructions before your test.

• One to two days before a colonoscopy, you will stop eating solid foods and drink only clear fluids, such as water, tea, coffee, clear juices, clear broths, Popsicles, and gelatin (such as Jell-O). Do not drink anything red or purple, such as grape juice or fruit punch. And do not eat red or purple foods, such as grape Popsicles or cherry Jell-O. Some new products, such as the Nutraprep meal kit or Visicol tablets or oral phospho-soda, are other methods of preparing for a colonoscopy. Ask your doctor whether another method will work for you.
• Your doctor may have you take a prescription laxative tablet or drink a laxative solution (such as Nulytely or Golytely) the evening before your colonoscopy. This solution will be given to you as a powder that you will mix with 1 gal (3.8 L) of water. You are often asked to drink this laxative solution over 1 to 2 hours. This solution may taste very salty and may make you feel sick to your stomach. To make your colon prep easier, you may want to try some of the following tips:
  • Each time you drink some of the solution, you may also drink some water or clear fluids (like apple juice) to help get rid of the salty taste in your mouth.
  • You may find it easier to drink the solution if you chill it in the refrigerator first.
  • Ask your doctor if it is okay for you to add flavored drink crystals (such as Crystal Light) to the solution.
  • Add lemon juice to the solution or suck on sliced lemon wedges after you take a drink.
• You will want to stay home the evening before the test because the colon prep will make you use the bathroom often.
• Drink plenty of clear fluids during the prep so you will not get dehydrated. This will also help clean out your colon completely after you finish the colon prep.
• Do not eat any solid foods after drinking the laxative solution.
• Stop drinking clear liquids 6 to 8 hours before the colonoscopy.
• Your doctor may have you use an enema 30 to 60 minutes before the test to completely clean out your colon.

Arrange to have someone take you home after the test because you may be given a medicine (sedative) to help you relax before the test.

How It Is Done

Colonoscopy may be done in a doctor's office, clinic, or a hospital. The test is most often done by a doctor who works with problems of the digestive system (gastroenterologist). The doctor may also have an assistant. Some family doctors, internists, and surgeons are also trained to do colonoscopy.

During the test, you may get a pain medicine and a sedative put in a vein in your arm (IV) . These medicines help you relax and feel sleepy during the test. You may not remember much about the test.

You will need to take off most of your clothes. You will be given a gown to wear during the test.

You will lie on your left side with your knees pulled up to your belly. The doctor will gently put a gloved finger into your anus to check for blockage. Then he or she will put the thin, flexible colonoscope in your anus and move it slowly through your colon. The doctor can look at the lining of the colon through the scope or on a computer screen hooked to the scope.

You may feel the need to have a bowel movement while the scope is in your colon. You may also feel some cramping. Breathe deeply and slowly through your mouth to relax your belly muscles. This should help the cramping. You will likely feel and hear some air escape around the scope. There is no need to be embarrassed about it. The passing of air is expected. You may be asked to change your position during the test.

Your doctor will look at the whole length of your colon as the scope is gently moved in and then out of your colon.

View a slideshow about how a colonoscopy is done.

The doctor may also use tiny tools, such as forceps, loops, or swabs, through the scope to collect tissue samples (biopsy) or take out growths. Usually, people do not feel anything if a biopsy is done or if polyps are taken out.

The scope is slowly pulled out of your anus and the air escapes. Your anal area will be cleaned with tissues. If you are having cramps, passing gas may help relieve them.

The test usually takes 30 to 45 minutes, but it may take longer, depending upon what is found and what is done during the test.

After the test, you will be watched for 1 to 2 hours. When you are fully awake, you can go home. You will not be able to drive or operate machinery for 12 hours after the test. Your doctor will tell you when you can eat your normal diet and do your normal activities. Drink a lot of fluid after the test to replace the fluids you may have lost during the colon prep but do not drink alcohol.

How It Feels

This test can be uncomfortable and you may feel embarrassed. The colon prep will cause diarrhea and cramping which may make you use the bathroom often during the night.

During the test, you may feel very sleepy and relaxed from the sedative and pain medicines. You may have cramping or feel brief, sharp pain when the scope is moved or air is blown into your colon. As the scope is moved up the colon, you may feel the need to have a bowel movement and pass gas. If you are having pain, tell your doctor.

The suction machine used to remove stool (feces) and secretions may be noisy but does not cause pain.

You will feel sleepy after the test for a few hours. Many people say they do not remember very much about the test because of the sedative.

After the test, you may have bloating or crampy gas pains and may need to pass some gas. If a biopsy was done or a polyp taken out, you may have traces of blood in your stool (feces) for a few days. If polyps were taken out, your doctor may instruct you to not take aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) for 7 to 14 days.

Risks

There is a small chance for problems from a colonoscopy. The scope or a small tool may tear the lining of the colon or cause bleeding.

After the test

After the test, call your doctor immediately if you:

• Have heavy rectal bleeding.
• Have severe belly pain.
• Develop a fever.
• Are very dizzy.
• Are vomiting.
• Have a swollen and firm belly.

Results

Colonoscopy is a test that allows your doctor to look at the inner lining of your large intestine (rectum and colon). If a sample of tissue (biopsy) was collected during the colonoscopy, it will be sent to a lab for tests.

• Samples of colon tissue are usually sent to a pathology lab, where they are looked at under a microscope for diseases.
• Other samples of colon tissue may be sent to a microbiology lab to see whether an infection is present.

Your doctor may be able to tell you the results immediately after the procedure. Other test results are ready in 2 to 4 days. Test results for certain infections may be ready in several weeks.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

• Having a barium enema within a week before the test. Barium can block your doctor's view of the colon.
• Having stool (feces) in the colon, a colon that has many turns, past surgery on the colon, or a lot of pain during the test.
• Taking iron supplements. This may make your stool turn black and make it hard to clean out the colon. Do not take iron supplements for several days before a colonoscopy.
• Drinking red or purple fluids, such as grape juice or fruit punch.
• Eating red or purple foods, such as grape Popsicles or cherry Jell-O.

What To Think About

• In general, pregnant women and people who have an abdominal infection or diverticulitis should not have a colonoscopy unless there is an important reason for it.
• Colonoscopy is a more expensive procedure than a barium enema and other endoscopic colon tests (such as proctoscopy or sigmoidoscopy), but it can be done less often over time if results are normal.
• Most experts, including the American Gastroenterological Association, recommend that people with no risk factors for colorectal cancer start screening tests at age 50.
• The American Gastroenterological Association recommends that people with a family history of colorectal cancer start screening tests at age 40, or 10 years before the age that the relative got cancer.
• If you are at increased risk for colon cancer, talk to your doctor about which test is best for you and how often you should have the test.

References

Other Works Consulted

• Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

• Levin B, et al. (2008). Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: A joint guideline from the American Cancer Society, the U.S. Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. CA: A Cancer Journal for Clinicians, 58(3): 130-160.

• Pagana KD, Pagana TJ (2006). Mosby's Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.

• U.S. Preventive Services Task Force (2002). Screening for colorectal cancer. Available online: http://www.ahrq.gov/clinic/uspstf/uspscolo.htm.

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