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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 the test, 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. (125 cm) to 72 in. (183 cm) long. A small video camera is attached to it 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 is worse than the test. The prep may be uncomfortable, and you may feel hungry on the clear liquid diet. 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.

Colonoscopy is one of the many tests that may be used to screen for colon cancer. Other tests include stool tests, sigmoidoscopy, and CT colonography. Which screening test you choose depends on what you prefer. Talk to your doctor about what puts you at risk and what test is best for you.

Why It Is Done

Colonoscopy is done to:

  • Check for polyps as a screening test for colorectal cancer.
  • 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 CT scan, MRI, virtual colonoscopy, stool test, or barium enema.
  • Watch or treat inflammatory bowel disease (IBD).
  • Check for the cause of long-term, unexplained belly pain.

How To Prepare

Procedures can be stressful. This information will help you understand what you can expect. And it will help you safely prepare for your procedure.

Preparing for the procedure

  • Be sure you have someone to take you home. Anesthesia and pain medicine will make it unsafe for you to drive or get home on your own.
  • Understand exactly what procedure is planned, along with the risks, benefits, and other options.
  • Tell your doctor ALL the medicines, vitamins, supplements, and herbal remedies you take. Some may increase the risk of problems during your procedure. Your doctor will tell you if you should stop taking any of them before the procedure and how soon to do it.
  • If you take aspirin or some other blood thinner, ask your doctor if you should stop taking it before your procedure. Make sure that you understand exactly what your doctor wants you to do. These medicines increase the risk of bleeding.
  • Make sure your doctor and the hospital have a copy of your advance directive. If you don't have one, you may want to prepare one. It lets others know your health care wishes. It's a good thing to have before any type of surgery or procedure.

Before the procedure

  • Follow your doctor's directions about when to stop eating solid foods and drink only clear liquids. You can drink water, clear juices, clear broths, flavored ice pops, and gelatin (such as Jell-O). Do not eat or drink anything red or purple. This includes grape juice and grape-flavored ice pops. It also includes fruit punch and cherry gelatin.
  • Drink the "colon prep" liquid as your doctor tells you. You will want to stay home, because the liquid will make you go to the bathroom a lot. Your stools will be loose and watery. It's very important to drink all of the liquid. If you have problems drinking it, call your doctor. Some doctors may have you take a tablet rather than drink a liquid.
  • Do not eat any solid foods after you drink the colon prep.
  • Stop drinking clear liquids 6 to 8 hours before the test.

How It Is Done

A colonoscopy may be done in a doctor's office, clinic, or a hospital.

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.

Before the test

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

You may lie on your left side with your knees pulled up to your belly. Because you will be given medicine during the colonoscopy, you probably won't remember much, if anything, until you wake up after the procedure.

Next, the doctor will insert a thin, flexible colonoscope in your anus and move it slowly through the rectum and into your colon. Air will be used to inflate your colon so the doctor can look at the lining of the colon through the scope or on a computer screen hooked to the scope.

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. You may be asked to change your position during the test.

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 don't 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.

After the test

After the test, you may need to stay at the clinic for 1 to 2 hours. Or you may be allowed to leave sooner with the person who will drive you home.

How long the test takes

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.

If a child is having the test, they can go home after the medicine wears off. This takes 1 to 2 hours.

How It Feels

The colon prep will cause diarrhea. Some people also have cramping.

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 that they don't remember very much about the test because of the sedative.

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.

Results

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 found.

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

Colonoscopy

Normal:

The lining of the colon looks smooth and pink, with a lot of normal folds. No growths, pouches, bleeding, or inflammation are seen.

Abnormal:

Some abnormal findings of colonoscopy include hemorrhoids (the most common cause of blood in the stool), polyps, cancer, one or more sores (ulcers), pouches in the wall of the colon (diverticulosis), and inflammation. A red, swollen lining of the colon (colitis) may be caused by infection or inflammatory bowel disease (IBD).

Credits

Current as of: April 29, 2020

Author: Healthwise Staff
Medical Review:
Adam Husney MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Kathleen Romito MD - Family Medicine
Arvydas D. Vanagunas MD - Gastroenterology

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