This test can find both colorectal polyps and cancer.

In this test, the doctor looks at the entire length of the colon and rectum with a colonoscope. It has a video camera on the end that is connected to a display monitor so the doctor can examine the inside of the colon. Special instruments can be passed through the colonoscope to remove (biopsy) suspicious looking areas such as polyps, if needed.

Before the test: You will need a bowel prep to clean out your lower colon and rectum. Most preps require strong laxatives, enemas, and/or special diets (such as drinking only clear liquids). Your doctor will give you specific instructions. Be sure your doctor is aware of your medications, as you may need to change how you take them before the test. You may need to arrange for someone to drive you home from the test because the sedative used can affect your ability to drive.

During the test: The test takes about 30 minutes—longer if a polyp is found and removed. Before the colonoscopy, you will be given a sedative to make you feel comfortable and sleepy. You may not be aware of what is going on and may not remember the procedure afterward.

You will be placed on your side with your knees flexed, and draped. Your blood pressure, heart rate, and breathing rate will be monitored. Your doctor should do a digital rectal exam before inserting the lubricated colonoscope. It is passed to the very beginning of the colon. The colonoscope will deliver air into the colon so that it is easier for the doctor to see the colon’s lining and use the instruments. To ease any discomfort it may help to breathe deeply and slowly through your mouth. The doctor will look at the inner walls of the colon as he or she slowly withdraws the colonoscope. If a small polyp is found, the doctor may remove it, usually done by passing a wire loop through the colonoscope to cut the polyp from the colon’s wall with an electrical current. The polyp can then be sent to a lab to check whether it has any areas that have changed into cancer. If your doctor sees a larger polyp or tumor, a biopsy may be done. A small bit of tissue is removed through the colonoscope and later examined to determine if it is a cancer, a benign (non-cancerous) growth, or a result of inflammation.

Possible side effects: Many people consider the bowel prep the most unpleasant part of the test, as it usually requires you to be in the bathroom quite a bit. The test may be uncomfortable, but the sedative usually prevents this. Some people may have gas pains or cramping after the test. Others may have low blood pressure or changes in heart rhythms due to the sedation, although these are rarely serious. If a polyp is removed or a biopsy is done during the colonoscopy, you may notice some blood in your stool for a day or two after the test.