Colonoscopy lets your doctor examine the lining of your large intestine (colon) for abnormalities by inserting a thin flexible tube, as thick as your finger, into your anus and slowly advancing it into the rectum and colon. This instrument, called a colonoscope, has its own lens and light source and it allows your doctor to view images on a video monitor.

Colonoscopy may be recommended as a screening test for colorectal cancer. Colorectal cancer is the third leading cause of cancer deaths in the United States. Annually, approximately 150,000 new cases of colorectal cancer are diagnosed in the United States and 50,000 people die from the disease. It has been estimated that increased awareness and screening would save at least 30,000 lives each year. Colonoscopy may also be recommended by your doctor to evaluate for symptoms such as bleeding and chronic diarrhea.

Your doctor will tell you what dietary restrictions to follow and what cleansing routine to use. In general, the preparation consists of limiting your diet to clear the liquids the day before and consuming either a large volume of special cleansing solution or special oral laxatives. The colon must be completely clean for the procedure to be accurate and comprehensive, so be sure to follow your doctor’s instructions carefully.

Most medications can be continued as usual, but some medications can interfere with the preparation or the examination. Inform your doctor about medications you’re taking, particularly aspirin products, arthritis medications, anticoagulants (blood thinners such as warfarin or heparin), clopidogrel, insulin or iron products. Also, be sure to mention the allergies you have to medications.

Colonoscopy is well-tolerated and rarely causes much pain. You might feel pressure, bloating or cramping during the procedure. Typically, your doctor will give you a sedative or painkiller to help you relax and better tolerate discomfort. You will lie on your side or back while your doctor slowly advances a colonoscope along your large intestine to examine the lining. Your doctor will examine the lining again as he or she slowly withdraws the colonoscope. The procedure itself usually takes less than 45 minutes, although you should plan on two to three hours for waiting, preparation and recovery.

If your doctor thinks an area needs further evaluation, he or she might pass an instrument through the colonoscope to obtain a biopsy to be analyzed. Biopsies are used to identify many conditions, and your doctor will often take a biopsy even if he or she doesn’t suspect cancer. If colonoscopy is being performed to identify sites of bleeding, your doctor might control the bleeding through the colonoscope by injecting medications or by cauterization (sealing off bleeding vessels with heat treatment) or by use of small clips. Your doctor might also find polyps during colonoscopy, and he or she will most likely remove them during the examination. These procedures don’t usually cause any pain.

Colonoscopy and polypectomy are generally safe when performed by doctors who have been specially trained and are experienced in these procedures. One possible complication is a perforation, or tear, through the bowel wall that could require surgery. Bleeding might occur at the site of biopsy or polypectomy, but it’s usually minor. Bleeding can stop on its own or be controlled through the colonoscope; it rarely requires follow-up treatment. Some patients might have a reaction to the sedatives or complications from heart or lung disease. Although complications after colonoscopy are uncommon, it’s important to recognize early signs of possible complications. Contact your doctor if you notice severe abdominal pain, fever, and chills, or rectal bleeding. Note that bleeding could occur several days after the procedure.

Important Reminder: This information is intended to provide general guidance. It does not provide definitive medical advice. It is very important that you consult your doctor about your specific condition.