Colonoscopy: What It Is and What to Expect

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

This test is special because it does two jobs at once. It can find growths called polyps. It can also remove them during the same visit. 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.

The doctor needs a clear view, so 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. It is not painful, just inconvenient, since you will spend time near a bathroom. Still, a clean colon really matters. 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.

On the day of the test, most people get sedation — medicine to help you relax or sleep lightly. It means 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. NIDDK says the exam itself usually takes less than an hour.

Does the doctor spot a polyp or another odd-looking area? They can often remove it right then through the colonoscope. This is called a polypectomy. The tissue goes to a lab and is looked at under a microscope. The lab checks 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.

Say you are at average risk and your colonoscopy comes back normal. Experts then recommend repeating the test every 10 years. That long gap works 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.

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 problems 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.

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

Coverage rules vary. So it is worth checking with your insurer before the test, so you know what you might owe.

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

• Call 911 or go to an emergency department if your belly pain turns severe after the exam, or bleeding from the anus does not stop, or you feel faint, dizzy or unusually weak.
• Call your care team the same day if bloody bowel movements keep coming rather than settling, or you run a temperature of 100.4°F (38°C) or higher in the days after a polyp was removed.
• Call your care team within a day or two if bloating and gas have not eased, or side effects stop you finishing the bowel prep before your appointment.

Source: NIDDK — Colonoscopy.