Colonoscopy is a screening test to view the interior lining of the large intestine (rectum and colon) through a thin, flexible tube fixed with a fibre optic camera called a colonoscope. This test is used to detect problems or diseases of the anus, rectum, or large intestine. This test is usually performed for evaluating the causes of abdominal pain, bleeding or pus in the stool, anemia, prolonged constipation or diarrhea and as a screen test for colon cancer or polyps. During a colonoscopy, tissue samples can be collected and abnormal growths can be removed.

Care before the test
This generally involves taking some kinds of laxatives prescribed by the doctor to cleanse out the colon one day prior to the test. It is better to avoid eating solid food and drink only clear fluids one or two days before the test. Inform your doctor whether you are taking medications like insulin, iron pills and any blood thinners, you are allergic to any medications, you have had an X-ray test using barium contrast material within the past 4 days, you are or might be pregnant and about any prior surgeries in the abdomen or a heart-valve infection that you have had. You may be advised to avoid taking aspirin or nonsteroidal anti-inflammatory drugs for several days before the test to reduce the risk of bleeding if any biopsy sample needs to be taken.

How the test is done
Before colonoscopy is done sedatives will be given to make the person more comfortable during the procedure. The person is made to lie on one side with knees flexed toward the abdomen. First a rectal exam with the finger is done and then the colonoscope is inserted through the anus into the large intestine. The instrument is advanced through the colon until it comes to the place where the colon meets the small intestine, on the right lower part of the abdomen. Then air is passed through the colonoscope to gently inflate the colon for a clear view of the entire circumference of the wall of the colon on a TV monitor. Additional sedatives may be given if needed.

If any abnormalities are seen, photographs and a biopsy or a tissue sample may be taken. Colonoscopy is also used to remove small colorectal polyps.

Risks
Complications from colonoscopy are rare. There is a slight risk of puncturing the colon or causing severe bleeding by damaging the wall of the colon and cardiac, respiratory and blood pressure problems. There is also a slight risk of causing a colon infection.

Age for testing
Screening test for colon cancer is recommended after age 50. Colonoscopy once every 5 or even 10 years is one way to have this screening done.