A colonoscopy is a test where a flexible fiber optic instrument is inserted into the colon, also called the large intestine. This instrument is called a colonoscope. It is a long, thin tube with a camera and light on the end. With it, a doctor can view the inner surface of the colon. The doctor can also sample or remove abnormal growths through the colonoscope.

Who is a candidate for the test?

A colonoscopy may be recommended for a person with:

A colonoscopy may also be recommended for someone at high risk for colorectal cancer. This may include a person who has a strong family history of colorectal cancer or polyps.

How is the test performed?

The person may be given medicine to make him or her drowsy or more comfortable during the procedure. The person lies on one side with knees flexed toward the abdomen. The doctor inserts the colonoscope through the anus and up into the large intestine. The instrument is pushed through the colon until it comes to the place where the colon meets the small intestine.

At that point, air is passed through the colonoscope to gently inflate the colon. This gives the doctor a clear view of the inner lining of the colon. The doctor then withdraws the instrument slowly, while examining all regions of the colon along the way. Places of interest on the interior of the colon are sometimes photographed.

If the doctor sees tissue that looks abnormal, a biopsy, which is a small tissue sample, may be taken. Small colorectal polyps can also be removed through the colonoscope.