A colonoscopy is an internal examination of the colon, using an instrument called a colonoscope. The colonoscope is a small camera attached to a flexible tube. Unlike sigmoidoscopy, which examines only the lower third of the colon, colonoscopy examines the entire length of the colon.

How the test is performed

You will lie on your left side with your knees drawn up toward the chest. After administration of a sedative and pain reliever, the colonoscope is inserted through the anus and gently advanced to the terminal small bowel.

Air will be inserted through the scope to provide a better view. Suction may be used to remove secretions.

Since better views are obtained during withdrawal than during insertion, a more careful examination is done during withdrawal of the scope. Tissue samples may be taken with tiny biopsy forceps inserted through the scope. Polyps may be removed with electrocautery snares, and photographs may be taken.

Specialized procedures, such as laser therapy, may also be performed.

How to prepare for the test

Thorough cleansing of the bowel is mandatory. Instructions for doing this will be given by the provider. This will include using enemas, not eating solid foods 2 or 3 days before the test, and taking laxatives. You may be told to stop taking aspirin or other blood-thinning medications for several days before the test.

To avoid dehydration, drink plenty of clear liquids such as juices and broths. Unless otherwise instructed, continue taking any regularly-prescribed medication. Discontinue taking iron preparations a few weeks before the test, unless otherwise instructed by the health care provider. Iron residues produce a dark black stool, which inhibits the view.

Complete emptying of the colon before the examination requires enemas or other purgatives. These must be repeated until no solid matter remains. An intravenous infusion and an injection will be given to administer a pain reliever and a sedative during the procedure.

People with valvular heart disease may receive antibiotics before and after the test to prevent infection. Outpatients must plan to have someone take them home after the test, as they will be woozy and unable to drive.

Infants and children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:

  • Infant test or procedure preparation (birth to 1 year)  
  • Toddler test or procedure preparation (1 to 3 years)  
  • Preschooler test or procedure preparation (3 to 6 years)  
  • Schoolage test or procedure preparation (6 to 12 years)  
  • Adolescent test or procedure preparation (12 to 18 years)

How the test will feel

The sedative and pain medication will provide relaxation and produce a drowsy feeling. A rectal examination usually precedes the test to dilate the rectum and make sure there are no major obstructions. You may have the urge to defecate when the rectal exam is performed or as the colonoscope is inserted.

You may feel pressure as the scope moves inside. Brief cramping and gas pains may be felt as air is inserted or as the scope advances. The passing of gas is necessary and should be expected.

Discomfort may be lessened by taking slow, deep breaths. This will also help relax the abdominal muscles. Mild abdominal cramping and considerable passing of gas may occur after the exam. Sedation should wear off in a few hours. Because of the sedation, you may not feel any discomfort and may have no memory of the test.

Why the test is performed

  • To obtain tissue specimen for biopsy  
  • To evaluate unexplained anemia  
  • To evaluate unexplained blood in the stool, abdominal pain, persistent diarrhea, or abnormalities (such as polyps) found on contrast x-rays (barium enema)  
  • To determine the type and extent of inflammatory bowel disease (ulcerative colitis and Crohn’s disease)  
  • To follow a previous finding of polyps, colon cancer, or a family history of colon cancer

Normal Values
Normal findings are simply healthy intestinal tissues.

What abnormal results mean

  • Lower gastrointestinal (GI) bleeding  
  • Polyps (which can be removed through the colonoscope during the exam)  
  • Tumor  
  • Inflammatory bowel disease  
  • Diverticulosis (particularly in older people)

Additional conditions under which the test may be performed:

  • CMV gastroenteritis or colitis  
  • Colon cancer screening  
  • Colorectal polyps  
  • Ischemic colitis  
  • Pseudomembranous colitis

What the risks are

  • Bowel perforation (hole), requiring an repair operation (less than 2 out of 1,000 tests)  
  • Heavy or persistent bleeding from biopsy or polypectomy sites (1 out of 1,000 tests)  
  • Adverse reaction to sedative medication causing respiratory depression or low blood pressure (4 out of 10,000 tests)  
  • Infection requiring antibiotic therapy (very rare)  
  • Nausea, vomiting, bloating, or rectal irritation caused by oral purgatives

Special considerations
You must sign an informed consent form. Several hours rest is recommended after the test. To replace fluids lost because of laxatives and fasting, drink plenty of liquids after the test.

Johns Hopkins patient information

Last revised: December 5, 2012
by David A. Scott, M.D.

Medical Encyclopedia

  A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | 0-9

All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.