Health Encyclopedia

Colonoscopy

Definition

A colonoscopy is an internal examination of the colon (large intestine), using an instrument called a colonoscope.

How the test is performed

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.

You will lie on your left side with your knees drawn up toward the chest. After you've received a sedative and pain reliever, the colonoscope is inserted through the anus and gently advanced to the lowest part of the 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 as the colonoscope is pulled back out, 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 done.

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. Stop 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 makes the view inside the bowel less clear.

People with heart valve 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 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
To obtain tissue specimen for biopsy
To screen for colorectal cancer; Americans at average risk should begin screening at age 50.

Normal Values

Normal findings are healthy intestinal tissues.

What abnormal results mean

Diverticulosis (abnormal pouches on the lining of the intestines, most often seen in older people)
Inflammatory bowel disease
Lower gastrointestinal (GI) bleeding
Polyps (which can be removed through the colonoscope during the exam)
Tumor

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 (a hole or tear in the wall of the colon), requiring a repair operation (fewer than 1 out of 1,000 tests)
Heavy or persistent bleeding from biopsy or polyp-removal sites (1 out of 1,000 tests)
Adverse reaction to sedative medication, causing breathing problems or low blood pressure (4 out of 10,000 tests)
Infection requiring antibiotic therapy (very rare)
Nausea, vomiting, bloating, or rectal irritation caused by medicines, taken by mouth, that cleanse the bowel

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.

References

Pasricha PJ. Gastrointestinal endoscopy. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 136.

Review Date:3/8/2008
Reviewed By:Christian Stone, MD, Division of Gastroenterology, Washington University in St. Louis School of Medicine, St. Louis, MO. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

ADAM Quality A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is the first of its kind, requiring compliance with 53 standards of quality and accountability, verified by independent audit. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial process. A.D.A.M. is also a founding member of Hi-Ethics (www.hiethics.com) and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

The Agency for Health Care Administration (Agency) and this website do not claim the information on, or referred to by, this site is error free. This site may include links to websites of other government agencies or private groups. Our Agency and this website do not control such sites and are not responsible for their content. Reference to or links to any other group, product, service, or information does not mean our Agency or this website approves of that group, product, service, or information.

Additionally, while health information provided through this website may be a valuable resource for the public, it is not designed to offer medical advice. Talk with your doctor about medical care questions you may have.