A colonoscopy is an exam used to look for changes in the large intestine (colon) and rectum — such as ulcers, polyps or cancer

During a colonoscopy, a long, flexible tube (colonoscope) is inserted into the rectum. A tiny video camera at the tip of the tube allows the doctor to view the inside of the entire colon. Sometimes the last part of small intestine which opens into the colon can also be examined.

Tissue samples (biopsies) can be taken during a colonoscopy. If necessary, polyps or other types of abnormal tissue can be removed through the scope during a colonoscopy.

Why it's done?

Your doctor may recommend a colonoscopy to:

Treat an issue. Sometimes, a colonoscopy may be done for treatment purposes, such as stopping bleeding, placing a stent or removing an object in your colon.

How you prepare?

Before a colonoscopy, you’ll need to clean out (empty) your colon. Any residue in your colon may make it difficult to get a good view of your colon and rectum during the exam.


To empty your colon, your doctor may ask you to:

Also tell your doctor if you take aspirin or any blood thinners like warfarin, newer anticoagulants, such as dabigatran or rivaroxaban, used to reduce risk of blot clots or stroke; or heart medications that affect platelets, such as clopidogrel.


You may need to adjust your dosages or stop taking the medications temporarily.


A colonoscopy poses few risks. Rarely, complications of a colonoscopy may include:

After discussing the risks of colonoscopy with you, your doctor will ask you to sign a consent form giving permission for the procedure.

What you can expect

During the procedure

During a colonoscopy, you’ll wear a gown, but likely nothing else. Sedation or anaesthesia is usually recommended, but it can be done without sedation also. In most cases, the sedative is combined with pain medication given directly into your blood stream (intravenously) to lessen any discomfort.


You’ll begin the exam lying on your side on the exam table, usually with your knees drawn toward your chest. The doctor will insert a colonoscope into your rectum.


The scope — which is long enough to reach the entire length of your colon — contains a light and a tube (channel) that allows the doctor to pump air, carbon dioxide or water into your colon. The air or carbon dioxide inflates the colon, which provides a better view of the lining of the colon.


When the scope is moved or air is introduced, you may feel stomach cramping or the urge to have a bowel movement.


The colonoscope also contains a tiny video camera at its tip. The camera sends images to an external monitor so that the doctor can study the inside of your colon.


The doctor can also insert instruments through the channel to take tissue samples (biopsies) or remove polyps or other areas of abnormal tissue.


A colonoscopy typically takes about 30 to 60 minutes.

After the procedure

After the exam, it takes about an hour to begin to recover from the sedative. You’ll need someone to take you home because it can take up to a day for the full effects of the sedative to wear off. Don’t drive or make important decisions or go back to work for the rest of the day.


You may feel bloated or pass gas for a few hours after the exam, as you clear the air from your colon. Walking may help relieve any discomfort.


You may also notice a small amount of blood with your first bowel movement after the exam. Usually this isn’t cause for alarm. Consult your doctor if you continue to pass blood or blood clots or if you have persistent abdominal pain or a fever.

When the exam is finished, the endoscope is slowly retracted through your mouth. An endoscopy typically takes 10-15 minutes.


Your doctor will review the results of the colonoscopy and then share the results with you.

Negative result

A colonoscopy is considered negative if the doctor doesn’t find any abnormalities in the colon.


Your doctor may recommend that you have another colonoscopy:

If there was residual stool in the colon that prevented complete examination of your colon, your doctor may recommend a repeat colonoscopy. How soon will depend on the amount of stool and how much of your colon was able to be seen. Your doctor may recommend a different bowel preparation to ensure that your bowel is completely emptied before the next colonoscopy.

Positive result

A colonoscopy is considered positive if the doctor finds any polyps or abnormal tissue in the colon.


Most polyps aren’t cancerous, but some can be precancerous. Polyps removed during colonoscopy are sent to a laboratory for analysis to determine whether they are cancerous, precancerous or noncancerous.


Depending on the size and number of polyps, you may need to follow a more rigorous surveillance schedule in the future to look for more polyps.


If your doctor finds one or two polyps less than 0.4 inch (1 centimeter) in diameter, he or she may recommend a repeat colonoscopy in 7 to 10 years, depending on your other risk factors for colon cancer.


Your doctor will recommend another colonoscopy sooner if you have:

If you have a polyp or other abnormal tissue that couldn’t be removed during the colonoscopy, your doctor may recommend a procedure to remove it or surgery.