Colonoscopy

Before the Test

Be sure your doctor knows about any medicines you are taking. You might need to change how you take them before the test. The colon and rectum must be empty and clean so your doctor can see their inner linings during the test. This can be done in many ways, but the most common involves drinking large amounts of a liquid laxative the evening before and the morning of the procedure. This leads to spending a lot of time in the bathroom. 

Your doctor will give you specific instructions. It’s important to read these carefully a few days ahead of time, since you may need to follow a special diet for at least a day before the test and to shop for supplies and laxatives. If you’re not sure about any of the instructions, call the doctor’s office and go over them with the nurse. 

You will be told not to eat or drink anything for at least 24 hours before your test. If you normally take prescription medicines in the morning, talk with your doctor or nurse about how to manage them for the day. 

Because a sedative is used during the test, you’ll need to arrange for someone you know to take you home from the test.

During the Test

The test itself usually takes about 30 minutes, but it may take longer if a polyp is found and removed. Before it starts, you’ll be given a sedating medicine (into a vein) to make you feel relaxed and sleepy during the procedure. You’ll wake up after the test is over, but might not be fully awake until later in the day. 

During the test, you’ll be asked to lie on your side with a drape covering you. Your blood pressure, heart rate, and breathing rate will be monitored during and after the test. 

Your doctor might insert a gloved finger into the rectum to examine it before putting in the colonoscope. The colonoscope is lubricated so it can be inserted easily into the rectum. Once in the rectum, the colonoscope is passed all the way to the beginning of the colon, called the cecum. 

The doctor will look at the inner walls of the colon as he or she slowly removes the colonoscope. If a small polyp is found, it may be removed. This is because some small polyps may become cancerous over time. Removing the polyp is usually done by passing a wire loop through the colonoscope to cut the polyp from the wall of the colon with an electric current. The polyp is then sent to a lab to be checked to see if it has any areas that have changed into cancer. 

If your doctor sees a larger polyp or tumor, or anything else abnormal, a biopsy may be done. A small piece of tissue is taken out through the colonoscope. The tissue is checked in the lab to see if it’s cancer, a benign (non-cancerous) growth, or a result of inflammation. 

You can read more about colonoscopy and sigmoidoscopy from the American Cancer Society in Frequently Asked Questions About Colonoscopy and Sigmoidoscopy.