Colonoscopy is a procedure in which a doctor uses a colonoscope or scope, to look inside your rectum and colon. Colonoscopy can show irritated and swollen tissue, ulcers, polyps, and cancer.

A colonoscopy can help a doctor find the cause of symptoms, such as

• bleeding from your anus
• changes in your bowel activity, such as diarrhea
• pain in your abdomen
• unexplained weight loss

Doctors also use colonoscopy as a screening tool for colon polyps and cancer. Screening is testing for diseases when you have no symptoms. Screening may find diseases at an early stage, when a doctor has a better chance of curing the disease.

Your doctor will recommend screening for colon and rectal cancer —also called colorectal cancer—starting at age 50 if you don’t have health problems or risk factors that make you more likely to develop colon cancer.

You have risk factors for colorectal cancer if you

• are male
• are African American
• or someone in your family has had polyps or colorectal cancer
• have a personal history of inflammatory bowel disease, such as ulcerative colitis and Crohn’s disease
• have Lynch syndrome, or another genetic disorder that increases the risk of colorectal cancer
• have other factors, such as that you weigh too much or smoke cigarettes

If you are more likely to develop colorectal cancer, your doctor may recommend screening at a younger age, and more often.

If you are older than age 75, talk with your doctor about whether you should be screened. For more information, read the current colorectal cancer screening guidelines from the U.S. Preventive Services Task Force (USPSTF).

Government health insurance plans, such as Medicare, and private insurance plans sometimes change whether and how often they pay for cancer screening tests. Check with your insurance plan to find out how often your plan will cover a screening colonoscopy.

To prepare for a colonoscopy, you will need to talk with your doctor, change your diet for a few days, clean out your bowel, and arrange for a ride home after the procedure.

Talk with your doctor

You should talk with your doctor about any health problems you have and all prescribed and over-the-counter medicines, vitamins, and supplements you take, including

• arthritis medicines
• aspirin or medicines that contain aspirin
• blood thinners
• diabetes medicines
• nonsteroidal anti-inflammatory drugs such as ibuprofen or naproxen
• vitamins that contain iron or iron supplements

Change your diet and clean out your bowel

A health care professional will give you written bowel prep instructions to follow at home before the procedure so that little or no stool remains in your intestine. A complete bowel prep lets you pass stool that is clear and liquid. Stool inside your intestine can prevent your doctor from clearly seeing the lining.

You may need to follow a clear liquid diet for 1 to 3 days before the procedure. You should avoid red and purple-colored drinks or gelatin. The instructions will include details about when to start and stop the clear liquid diet. In most cases, you may drink or eat the following:

• fat-free bouillon or broth
• gelatin in flavors such as lemon, lime, or orange
• plain coffee or tea, without cream or milk
• sports drinks in flavors such as lemon, lime, or orange
• strained fruit juice, such as apple or white grape—avoid orange juice
• water

Different bowel preps may contain different combinations of laxatives—pills that you swallow or powders that you dissolve in water or clear liquids. Some people will need to drink a large amount, often a gallon, of liquid laxative over a scheduled amount of time—most often the night before and the morning of the procedure. Your doctor may also prescribe an enema.

The bowel prep will cause diarrhea, so you should stay close to a bathroom. You may find this part of the bowel prep hard; however, finishing the prep is very important. Call a health care professional if you have side effects that keep you from finishing the prep.

Your doctor will tell you how long before the procedure you should have nothing by mouth.

Arrange for a ride home

For safety reasons, you can’t drive for 24 hours after the procedure, as the sedatives or anesthesia need time to wear off. You will need to make plans for getting a ride home after the procedure.

A doctor performs a colonoscopy in a hospital or an outpatient center. A colonoscopy usually takes 30 to 60 minutes.

A health care professional will place an intravenous (IV) needle in a vein in your arm or hand to give you sedatives, anesthesia, or pain medicine, so you won’t be aware or feel pain during the procedure. The health care staff will check your vital signs and keep you as comfortable as possible.

For the procedure, you’ll lie on a table while the doctor inserts a colonoscope through your anus and into your rectum and colon. The scope inflates your large intestine with air for a better view. The camera sends a video image to a monitor, allowing the doctor to examine your large intestine.

The doctor may move you several times on the table to adjust the scope for better viewing. Once the scope reaches the opening to your small intestine, the doctor slowly removes the scope and examines the lining of your large intestine again.

During the procedure, the doctor may remove polyps and will send them to a lab for testing. You will not feel the polyp removal. Colon polyps are common in adults and are harmless in most cases. However, most colon cancer begins as a polyp, so removing polyps early helps to prevent cancer.

If your doctor finds abnormal tissue, he or she may perform a biopsy. You won’t feel the biopsy.

After a colonoscopy, you can expect the following:

• The anesthesia takes time to wear off completely. You’ll stay at the hospital or outpatient center for 1 to 2 hours after the procedure.
• You may feel cramping in your abdomen or bloating during the first hour after the procedure.
• After the procedure, you—or a friend or family member—will receive instructions on how to care for yourself after the procedure. You should follow all instructions.
• You’ll need your pre-arranged ride home, since you won’t be able to drive after the procedure.
• You should expect a full recovery and return to your normal diet by the next day.

After the sedatives or anesthesia wear off, your doctor may share what was found during the procedure with you or, if you choose, with a friend or family member.

If the doctor removed polyps or performed a biopsy, you may have light bleeding from your anus. This bleeding is normal. A pathologist will examine the biopsy tissue, and results take a few days or longer to come back. A health care professional will call you or schedule an appointment to go over the results.

The risks of colonoscopy include

• bleeding
• perforation of the colon
• a reaction to the sedative, including breathing or heart problems
• severe pain in your abdomen
• death, although this risk is rare

A study of screening colonoscopies found roughly 4 to 8 serious complications for every 10,000 procedures.

Bleeding and perforation are the most common complications from colonoscopy. Most cases of bleeding occur in patients who have polyps removed. The doctor can treat bleeding that happens during the colonoscopy right away.

You may have delayed bleeding up to 2 weeks after the procedure. The doctor can diagnose and treat delayed bleeding with a repeat colonoscopy. The doctor may need to treat perforation with surgery.

Colorectal cancer is the second-leading cause of cancer death nationwide. But it can usually be cured when caught early. Screening tests like colonoscopy can save lives by catching problems before symptoms even appear, when treatments might work best.

So no matter how busy you feel, if you’re age 50 or older—or even younger if you’re at high risk—you should make time to talk with your doctor about getting screened for colorectal cancer.

“Screening is effective, and it’s been shown through clinical studies to reduce deaths,” says Dr. Carrie Klabunde, an NIH expert in cancer screening and prevention.

But although screening is known to save lives, many Americans ages 50 and older don’t get screened for colorectal cancer. The most common reason, says Klabunde, is that “people don’t realize this screening is something they need to do.” Other common reasons include costs and inconvenience, such as taking time off from work.

Colorectal cancer is cancer of the colon or rectum, both of which are part of the large intestine. Scientists don’t yet know what causes colorectal cancer, but certain factors affect your risk. Smoking, excess weight, or having 3 or more alcoholic drinks per day raises your risk.

“The risk for colorectal cancer rises with age,” Klabunde adds. Your risk also doubles if you have a close relative who had colorectal cancer.

The 3 recommended tests for colorectal cancer are colonoscopy, flexible sigmoidoscopy, or home stool tests. Each test has different benefits and drawbacks. Your health care provider may recommend one or more of these options.

Colonoscopy is the most accurate. The day before the test, you need to drink a special liquid or take prescription pills to cleanse your colon. A doctor inserts a tiny camera attached to a long, thin, flexible tube into the rectum and colon. Any growths the doctor sees, including polyps, can be removed during the procedure. Most polyps are harmless (benign), but some (called adenomas) can become cancer.

Flexible sigmoidoscopy also uses a camera attached to a tube, but the exam looks only at part of the large intestine. To prepare, you’ll need to have an enema (an injection of water into the rectum to cleanse the colon) the night before or the day of the procedure. Sigmoidoscopy may let you know if there’s a reason to have a colonoscopy.

Another option is a home stool test. You can take this test in the privacy of your home using inexpensive or free kits from your doctor’s office or pharmacy. After collecting a small sample of your stool, you mail or deliver it to a doctor or lab, where it will be tested for tiny amounts of blood, which could signal a problem.

Another screening test, called virtual colonoscopy or CT colonography, can scan the colon from the outside. But its effectiveness is still under study.

Don’t wait for symptoms to appear. Talk with a health care provider about when you should begin screening for colorectal cancer and, if so, which test(s) to get. And check with your health insurance company to see if screening costs are covered (they usually are).

What To Ask About Colorectal Screening

Everyone ages 50 to 75 (and younger people at increased risk) needs to have a plan for colorectal cancer screening. Ask your doctor:

• When should I start getting screened for colorectal cancer?
• Which screening test do you recommend for me?
• How can I prepare for the test?
• What should I expect during the test?
• Are there any risks involved?
• Who will perform the exam?
• Will I need someone to come with me?
• Who will give me the results, and when?