Colonoscopy: What It Is and What to Expect

The simple versionExplain▾

A colonoscopy lets a doctor look at the entire lining of your colon and rectum using a colonoscope — a thin, flexible tube with a light, a camera, and a small tool for removing tissue. The tube is gently passed through the anus into the rectum and up through the whole colon.

What makes this test special is that it does two jobs at once. It can find growths called polyps, and it can remove them during the same visit. Because certain polyps can slowly turn into cancer over years, taking them out can stop cancer before it ever starts.

Colonoscopy is the only common screening test that can both detect and prevent colorectal cancer in one procedure.

Getting ready: the prepExplain▾

For the doctor to see clearly, your colon has to be completely empty. In the day or two before the test you will:

• Change your diet, usually switching to clear liquids the day before
• Adjust certain medications, if your team tells you to
• Drink a special liquid bowel prep that causes watery bowel movements to flush the colon clean

Most people say the prep is the hardest part — not painful, just inconvenient, since you will spend time near a bathroom. A clean colon really matters, though. If the prep is incomplete, the doctor may miss something or have to repeat the test.

A thorough prep is what makes the exam accurate — follow the instructions exactly.

During the examExplain▾

On the day of the test, most people receive sedation — medicine to help you relax or sleep lightly — so you feel little or no discomfort. The doctor gently pumps a little air into the colon to open it up and see the lining better. The exam itself usually takes around 30 minutes.

If the doctor spots a polyp or other abnormal area, they can often remove it right then through the colonoscope. This is called a polypectomy. The tissue is sent to a lab and looked at under a microscope to check whether any abnormal or cancer cells are present.

Because of the sedation, you will need someone to drive you home. You may feel bloated or gassy for a short while as the air leaves your system.

How often you need itExplain▾

For people at average risk whose colonoscopy comes back normal, experts recommend repeating the test every 10 years. That long gap is possible because colonoscopy examines the whole colon and removes polyps along the way.

Your timing may be different if:

• Polyps were found and removed
• You have a family history of colorectal cancer
• You have an inherited condition such as Lynch syndrome
• You have inflammatory bowel disease

In those cases, your doctor may suggest starting earlier or coming back more often.

Ten years is the standard interval only for average-risk people with a normal result — your doctor will set the right schedule for you.

Weighing the risksExplain▾

Colonoscopy is generally safe, but like any procedure it carries some risk. The main ones are:

• Bleeding, most often after a polyp is removed
• A tear (perforation) in the wall of the colon, which is uncommon but serious

These complications happen in a small number of cases. Your care team will explain the specific risks to you before the test so you can make an informed choice.

Costs and coverageExplain▾

Colorectal cancer screening is a preventive service that many health plans, the Health Insurance Marketplace, and Medicare are required to help cover. One thing to know: if a colonoscopy is done to follow up on another positive screening test, or if a polyp is removed during a screening exam, some insurers may treat it as a diagnostic exam and bill differently.

Because coverage rules vary, it is worth checking with your insurer before the test so you understand what you might owe.

Ask your plan how a screening colonoscopy is covered — and what changes if a polyp is found.