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Screening Methods for Colorectal Cancer

Medically reviewed by Christina Chun, MPH on October 23, 2017Written by Ann Pietrangelo on October 23, 2017
colorectal cancer screening

Why screening matters

Colorectal cancer is the second leading cancer killer in the United States. But with routine screening, it’s a type of cancer that can be found and treated early.

Colorectal cancer starts in the colon or rectum, usually involving abnormal tissue growth called polyps. Polyps are quite common in people over age 50. It can take 10 to 15 years for a polyp to develop into colorectal cancer.

Screening tests can detect polyps, which a doctor can remove before they develop into cancer.

The U.S. Preventive Services Task Force (USPSTF) recommends screening for colorectal cancer beginning at age 50. If you’re at high risk of colorectal cancer, your doctor may advise you to start earlier.

In addition to age, other risk factors include a family history of this cancer or having an inflammatory bowel disease (IDB). Being sedentary, eating a low-fiber, high-fat diet, and using tobacco are a few lifestyle factors that influence risk for this cancer.

A variety of tests can be used to screen for colorectal cancer. Your doctor can help you decide which is the best option for you.

Colonoscopy

A colonoscopy allows your doctor to inspect your rectum and all of your colon.

Your entire colon must be clean. Your doctor will give you specific instructions on how to cleanse your colon before the procedure.

For the colonoscopy, you lie on your side with your knees drawn up toward your chest. You’re be given an intravenous sedative.

Your doctor uses a flexible, lighted tube (colonoscope) with a tiny camera on the end. They insert the tube into your rectum and colon. The doctor can examine the images on a screen. Air is pumped in to allow a clear view. The process takes about half an hour or so, and you’ll be able to go home within a few hours.

If any suspicious tissue or polyps are found, your doctor can use special instruments to remove them during the same procedure. Samples of the tissue are then sent to a laboratory so they can be examined for cancer.

If everything looks healthy, your doctor will likely suggest that you have another colonoscopy in 10 years. If polyps were found, or if you’re at a particularly high risk of colorectal cancer, you might be advised to have another one sooner.

A colonoscopy is considered to be safe. In rare cases, the colon or rectum is perforated, which can lead to serious complications.

Virtual colonoscopy

Computed tomography (CT) colonography is also known as a virtual colonoscopy.

As with a colonoscopy, you have to prepare by cleaning out your colon. It does require that a tube be inserted into your rectum to pump air inside. But sedation isn’t necessary.

Special X-ray equipment then rotates around the table, taking a series of images of the colon and rectum. A computer puts the images together to create a detailed picture for analysis. The test takes about 10 minutes.

There’s a lower risk of complications than with a colonoscopy. On the other hand, if abnormal growths or polyps are found, you’ll need a standard colonoscopy to have them removed and tested for cancer.

Sigmoidoscopy

In a sigmoidoscopy, your doctor can examine your rectum and sigmoid colon, which is the lower part of your colon. This test won’t detect abnormal tissue in the upper half of the colon.

A flexible, lighted tube with a small camera on the end (sigmoidoscope) is inserted into your rectum and colon. Your doctor can view the images on a screen. The tool only reaches two feet, so only about half of your colon is viewable.

You don’t have to clear your entire colon as with a colonoscopy, but you still have to cleanse your bowels before the test. You can be sedated, but it’s not usually required. The test takes 10 to 20 minutes.

The risk of perforation is small. Your doctor can remove abnormal tissue and polyps during this procedure. If the tissue is found to be cancerous, your doctor will likely recommend a colonoscopy to look at the upper half of your colon.

Fecal occult blood test (FOBT)

Because polyps and colorectal cancer can cause bleeding, your stool can be checked for small amounts of blood that you wouldn’t see otherwise.

A guaiac FOBT (gFOBT) uses a chemical to find blood in your stool.

Your doctor will instruct you avoid certain foods, such as red meat. You will also be told to stay away from certain medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, for a day or two before the test.

A fecal immunochemical (FIT) test relies on antibodies to detect blood in your stool.

For either test, you’ll use a special kit to collect multiple stool samples to return to a laboratory.

If blood is found in the stool, it doesn’t necessarily mean you have colorectal cancer. Other causes include hemorrhoids, ulcers, and diverticulosis. You’ll need additional testing, such as a colonoscopy, to determine the cause.

These tests can be repeated every year.

Stool FIT-DNA test

In addition to detecting blood, the FIT-DNA stool test can detect nine DNA biomarkers in three genes found in colorectal cancer and precancerous tissue.

This test requires that you collect your stool. You’ll be given a stool collection kit and instructions on how to return it to the laboratory.

If the test is negative, it should be repeated every three years. A positive result doesn’t confirm colorectal cancer. Other tests, such as a colonoscopy, can help your doctor learn more.

Air contrast barium enema

This test is also called double-contrast barium enema (DCBE), barium enema with air contrast, or lower GI series.

It involves taking laxatives or enemas to clean your bowels before the exam. Then barium sulfate and air are introduced into your rectum and colon. This highlights abnormal areas on X-ray images. The test can take from 30 to 45 minutes. Sedation isn’t necessary.

This procedure may not be sensitive enough to detect small polyps or cancers. But it may be an option if you can’t have a colonoscopy.

If anything suspicious is found, you’ll need additional testing to determine the cause.

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