Screening for Colorectal Cancer

The purpose of screening is early diagnosis and treatment. Screening tests are usually administered to people without current symptoms, but who may be at high risk for certain diseases or conditions.

Screening Tests

Fecal Occult Blood Test —A small sample of stool is placed on a special card. It is then tested by a lab for hidden blood. Blood can be present in the stool for many reasons. Colorectal cancer will not always cause blood in the stool. If positive, the test should be followed up with a more specific test such as endoscopy. A negative result does not guarantee that colorectal cancer is not present. Usually multiple samples are collected.

Sigmoidoscopy —A sigmoidoscope is a thin, lighted tube with a tiny camera attached. It is inserted into the rectum to view the inside of the lower colon and rectum. The doctor will use it to search for polyps, tumors, or abnormal growths.

Colonoscopy —A thin, lighted tube with a tiny camera attached is inserted into the rectum. The inside of the entire colon and rectum are examined. If a polyp or abnormal tissue is discovered, it may be removed and reviewed for further testing. For most patients, this is the standard for examining the colon.

Barium Enema —A barium liquid is put into the rectum by way of the anus. Barium is a metallic compound that helps highlight the image of the lower gastrointestinal tract on an x-ray.

CT colonography —A type of CT scan that uses computer software along with CT imaging to examine to colon for polyps. A rubber catheter is used to introduce air into the colon.

MR colonography —Magnetic imaging allows for examination of the entire colon. Water is used to expand the size of the colon.

Fecal Immunochemical Test —Like a fecal occult blood test, a sample of stool is placed on a special card. It is tested for hidden blood that reacts to a protein found in red blood cells. Blood from the upper part of the gastrointestinal tract, like the stomach, is not as likely to be detected. Unlike the fecal occult blood test, there is no dietary preparation required before taking the test.

Stool DNA Test —DNA cells are analyzed in a stool sample instead of blood. Colorectal cancer or polyp cells can be found in the stool. DNA tests look for genetic changes in the cells.

Screening Guidelines

The decision to screen will likely be made on an individual basis based on your risk factors. Most guidelines suggest the following:

For people at average risk

Beginning at age 50 (age may be younger for African Americans and Native Americans), use one of the following methods:

  • Colonoscopy every 10 years
  • Flexible sigmoidoscopy every 5 years
  • CT colonography every 5 years
  • Double-contrast barium enema every 5 years
  • MR colonography every 5 years
  • Stool DNA test every 3 years
  • Annual fecal occult blood test (FOBT)
  • Annual fecal immunochemical test (FIT)

For people with a first-degree relative with onset of colorectal cancer after age 60

  • Begin screening at age 40
  • Preferred screening: Colonoscopy every 10 years or more frequently, depending on the colonoscopy findings

For people with a first-degree relative with onset of colorectal cancer before age 60

  • Begin screening at age 40 or 10 years younger than age of diagnosis of the affected relative (whichever is first)
  • Preferred screening: Colonoscopy every 5 years


Please note, not all procedures included in this resource library are available at Allegiance Health or performed by Allegiance Health physicians.

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