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Getting Screened

Reviewed by: Mark B. Pochapin, M.D.
Last reviewed: March 31, 2011

Cancer of the colon and rectum, called colorectal cancer, is the second-leading cancer-related killer in the United States. But it doesn't have to be. Colorectal cancer is one cancer that is, in many cases, preventable. This is because most colorectal cancers begin as a small non-cancerous growth, called a polyp, in the colon or rectum. A particular type of polyp--called an adenomatous polyp or adenoma--can sometimes turn into cancer. Because it generally takes a non-cancerous adenomatous polyp several years to turn into cancer, regular colorectal cancer screening can be used to find and remove a polyp before cancer ever develops.

This is why screening--getting tested before symptoms occur--is so important. By the time you feel the symptoms of disease, cancer has already developed.

Who Should Be Screened and When?
Comparing Screening Tests
Before the Colonoscopy: Bowel Preps
Finding a Colonoscopy Doctor
Endoscopy Suite: Virtual Tour

Who Should Be Screened and When?

Those at Average Risk (do not have risk factors)
Women and men at average risk for colorectal cancer need to begin screening for colorectal cancer at age 50. American Cancer Society-Multisociety Task Force-American College of Radiology joint screening recommendations for those at average risk, include one of the seven options, categorized by tests that screen for both cancer and potentially pre-cancerous polyps or primarily for cancer:

Tests That Detect Polyps and Cancer
  • Colonoscopy every 10 years; OR
  • Flexible sigmoidoscopy every 5 years; OR
  • Double-contrast enema every 5 years; OR
  • Computed tomographic colonography (virtual colonoscopy) every 5 years.
Tests That Detect Primarily Cancer
  • Guaiac-based fecal occult blood test (FOBT) every year; OR
  • Fecal immunochemical test (FIT) every year; OR
  • Stool DNA test (interval uncertain).

People At Increased Risk (do have certain risk factors)

Women and men who have certain risk factors--such as a personal or family history of colorectal polyps or colorectal cancer or a personal history of inflammatory bowel disease--need to talk with their doctor about getting screened at an earlier age and with greater frequency.

Comparing Screening Tests

Flexible sigmoidoscopy
Double-contrast barium enema
Computed tomographic colonography
Fecal occult blood test and fecal immunochemical test
Stool DNA test


A colonoscopy is the most comprehensive screening test available, and the only test that allows both the detection and removal of any polyp or early cancer that is found. This screening test requires preparation with a clear liquid diet and oral laxative agent the day before, to cleanse the colon and rectum. The procedure itself involves the placement of colonoscope--a long, thin tube complete with tiny camera and light source--through the rectum and throughout the entire colon. The camera in the colonoscope transmits a video image of the lining of the colon and rectum to a television screen, which the doctor observes for polyps, cancer, or other abnormality. If the doctor sees any polyps or early cancer, he or she can use the colonoscope to remove the abnormal tissue during that same procedure. The tissue will then be sent to a laboratory to examine for cancer cells. People having a colonoscopy first undergo sedation--using a medication to make them sleepy--to minimize any discomfort. Complications with colonoscopy are very rare, but may include perforation of the colon, bleeding, or a reaction to the sedative medication. A colonoscopy should be performed by a gastroenterologist or surgeon who is specially trained in this procedure.

Flexible sigmoidoscopy

The flexible sigmoidoscopy is a screening test used to find colorectal cancer and polyps in the rectum and lower part of the colon; to pinpoint the cause of diarrhea or rectal bleeding; or to diagnose certain types of inflammatory bowel disease. Before you undergo this test, you must take a bowel prep regimen to cleanse the lower colon and rectum. Your doctor will prescribe this bowel prep regimen for you, but it usually consists of one or two enemas a few hours before the test. The test itself involves placement of a long, flexible tube--complete with camera and light source--through the rectum and throughout the lower portion of the colon. No sedation is used during this procedure. A flexible sigmoidoscopy is effective in detecting polyps and early cancers in these areas. However, a flexible sigmoidoscopy does not allow for the detection of polyps or cancers in the upper or right side of the colon. A flexible sigmoidoscopy is performed by a primary care physician or gastroenterologist. Complications with this procedure are exceedingly rare, and may include bowel perforation and bleeding.

Double-contrast barium enema

The double-contrast barium enema is one of the oldest tests used to evaluate the colon and rectum. The day before this test, you will need to follow a clear-liquid diet, and take a laxative to clear out your intestinal tract. This prep is not quite as powerful as the prep given before a colonoscopy. Just before the test, you will need to have a cleansing enema. As part of double-contrast barium enema itself, you will undergo another enema, using a tube that contains barium. The barium coats your lower digestive tract and, using an x-ray machine, allows the imaging of a clear silhouette of the colon's shape and condition. This x-ray image allows the viewing of large polyps or cancers. However, if any abnormalities are detected, a follow-up colonoscopy is needed to biopsy or remove the tissue. In an article in the New England Journal of Medicine, barium enema was found to be inferior to a colonoscopy for detecting polyps and growths. This test is performed by a radiologist, and is virtually risk-free, although it can aggravate ulcerative colitis or irritate the lining of your colon.

Computed tomographic colonography

The CT colonography, also called virtual colonoscopy, is a new technique for colorectal cancer screening. With this procedure, a device is inserted at the opening of the rectum, where a large balloon is inflated to fill the area with air so that the colon and rectum can be viewed with a CT scanner. Special computer software transforms the CT scan into a three-dimensional view of the colon and rectum. No tube is threaded through your colon, making the CT colonography less invasive than a colonoscopy, with little risk of bowel injury or bleeding. The same bowel prep required for a colonoscopy is also needed for a CT colonography. If a polyp or cancer is found during the CT colonography, a follow-up colonoscopy is needed to remove or to biopsy the abnormal tissue.

Fecal occult blood test and Fecal immunochemical test

A fecal occult blood test (FOBT), or guaiac FOBT, is performed annually and has been shown to reduce the death rate from colorectal cancer by 33%. The FOBT is a take-home test involving the placement of three stool samples on a card that is then sent to a laboratory for testing. Before an FOBT test, you must avoid red meat, citrus fruit, radishes, vitamin C supplements, aspirin, iron, and other substances known to sway the results of the test. You will need to read the test instructions carefully, noting foods, medications, and supplements that you should avoid. The FOBT works by detecting the presence of microscopic blood in the stool. This is because colorectal cancers can sometimes cause a small amount of bleeding that cannot be detected visually. However, other conditions can also cause such bleeding. If the test results show blood in the stool, a colonoscopy is needed to identify and treat the source of the bleeding. The FOBT test is done in the privacy of your own home, and is easy, painless, and inexpensive.

The fecal immunochemical test (FIT) also must be performed annually and acts to detect microscopic blood in the stool. Unlike the FOBT, the FIT does not require any dietary restrictions before the test. If the test results show blood in the stool, a colonoscopy is needed to identify and treat the source of the bleeding. Like the FOBT test, the FIT is done in the privacy of your own home, is easy, and is painless.

Both of these stool tests must be performed every year to be effective. In addition, they must be performed as a take-home, multiple-sample test. A stool test done with one sample, or done during a rectal examination at the doctor's office, is NOT effective as a screening test for colorectal cancer.

Stool DNA test

A new type of screening test is the stool DNA test. This test involves the use of a stool sample to evaluate for the presence of DNA related to colorectal cancer. If the results of this test are abnormal, a follow-up colonoscopy is needed. Like the FOBT and FIT, this test is done in the privacy of your own home, is easy, and is painless.

Before the Colonoscopy: Bowel Preps

If you are scheduled to have a colonoscopy, you will need to begin preparing for the procedure the day before. This is because the colon and rectum must be cleansed of any stool, to allow the doctor to view the inside of the colon and rectum clearly during the colonoscopy. First, you must begin a clear liquid diet, beginning the day before your colonoscopy. Second, you need to use a bowel preparation agent, or oral laxative. There is no pain or cramping involved with the prep, just a lot of trips to the bathroom.

Several bowel preparations are available. At the time that your colonoscopy appointment is made, you need to talk with your doctor about which bowel prep is right for you.

The Clear Liquid Diet

The most widely used diet for colon preparation is a clear liquid diet, followed the day before you have your colonoscopy. On this diet, you eat and drink clear liquids only. These include:

  • Chicken broth or beef broth (not bouillon because it can leave residue in your colon)
  • Light-colored Jello (not purple, red, orange, or green in color)
  • Clear fruit juice that you can see through, such as white grape juice, white cranberry juice, or apple juice
  • Water
  • Flavored waters
  • Coffee or tea, black or with sugar

So that you don't feel deprived or hungry during the day of your prep, it is a good idea to fix yourself a big bowl of Jello, along with a large bowl of broth and a tall glass of clear fruit juice for breakfast, lunch, and dinner. Chicken broth is a particularly good choice for dinner because the nutrients within it have a healing effect on the body. Be sure to avoid milk, milk products, powdered creamers, and red, orange, green, or purple-colored juices or Jello. These will color the lining of your colon and rectum, and your doctor may not be able to see any polyps or other abnormalities clearly.

Finding a Colonoscopy Doctor

If you are ready to undergo your screening colonoscopy, you will need to make sure you find a gastroenterologist or surgeon, specially trained in performing colonoscopy procedures. Your primary care physician or gynecologist should be able to refer you to such a doctor. If you need further assistance in locating a doctor trained in colonoscopy, the American Society for Gastrointestinal Endoscopy, or ASGE, can help!

The ASGE is a professional organization of doctors who specialize in performing colonoscopy and other GI endoscopic procedures. The Monahan Center is working closely with the ASGE to promote colorectal cancer screening and to make sure you can find a good colonoscopy doctor in your area!

You can search for an ASGE doctor in your area at:

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