Colon Cancer

What Screening Tests Are Available For Colon Cancer?

Screening for colorectal cancer involves special tests performed on people who have no symptoms of a particular illness.

Good screening tests are:

  • Safe
  • Relatively inexpensive
  • Proven effective in detecting the disease at an early stage and reducing the death rate from that disease

Current screening tests for colorectal cancer meet these four requirements and include:

Digital Rectal Exam

During a digital rectal examination (DRE) the doctor inserts a gloved, lubricated finger into the rectum to check for abnormalities. This is a routine part of a physical examination and commonly used to screen for colorectal cancer.

This test is effective in detecting rectal cancer; however, doctors are able to detect only 7 to 10 percent of colorectal cancers since most of the colon cannot be felt by the examiner’s finger. The goal of colorectal cancer screening is to detect the cancer before it grows large enough to be felt during such an exam.

By itself, the digital rectal exam is not considered an ideal screening test for colorectal cancer, but rather is used along with other screening tests.

Fecal Occult Blood Test (FOBT)

The fecal occult blood test (FOBT), also called the stool blood test or the guaiac test, is used to detect tiny amounts of blood in a stool sample. This test detects small amounts of blood in the stool that would not be visible.

Stool samples are smeared onto special cards and dropped off at the doctor’s office or a laboratory. This is done because tumors may bleed on one day and not the next; therefore, blood may be present in stool on one day and not the next. When colorectal cancer is present, the blood may be dark, or mixed with stool, but you often can’t see it. For this reason, the FOBT is important.

Need To Know:

Blood in the stool does not always mean you have colorectal cancer. Other causes include:

  • Bleeding ulcers
  • Inflammation of the stomach or gastritis
  • Inflammatory bowel disease (IBD)
  • Hemorrhoids

If fecal blood is found, additional tests are done to rule out cancer. Cancer can still be present if the FOBT is negative. This can happen if there was no bleeding when the test was performed. The results may come back negative but cancer is present. This is known as a false negative test.

Flexible Sigmoidoscopy Procedure

During a sigmoidoscopy procedure the doctor inserts a soft flexible, fiberoptic scope into the anus. The walls of the rectum and sigmoid portion of the colon are checked for tumors. A flexible sigmoidoscopy procedure may detect:

  • About half of all colon tumors
  • Nearly all rectal tumors

If doctors discover a growth or tumor during this procedure, abiopsy will be performed. During a biopsy, a small tissue sample is removed and then prepared for examination under a microscope. The biopsy procedure does not hurt.


A colonoscopy is similar to a sigmoidoscopy but is a more thorough examination of the entire colon. Patients receive medications that help them relax during the procedure. A flexible scope with a tiny camera attached is gently guided from the anus through the colon. Looking at the images provided by the camera on a monitor, the doctor examines the inside of the colon for any signs of inflammation, disease, or polyps. During the procedure, the doctor can take a sample of any suspicious areas for further testing, and can remove any polyps that are discovered.

How-To Information:

Colon Cancer Screening Guidelines

Seventy to 80 percent of all colon cancers occur in adults without known risk factors. The American Cancer Society guidelines recommend adults should begin colon cancer screening by age 50 years, either with:

  • Annual stool occult blood stool tests, sigmoidoscopy, and digital rectal exam every five years, or
  • Colonoscopy and digital rectal exam every 10 years, or
  • Double-contrast barium enema and DRE every five to 10 years.

Some experts recommend beginning blood stool tests and a digital rectal exam at age 40. For those who undergo periodic evaluation of the entire colon, no annual FOBT is needed.

Those at higher-than-average risk for colon cancer should consult their doctor to begin screening at an earlier age. Their doctors will probably recommend more thorough screening tests, including a colonoscopy or barium enema rather than sigmoidoscopy.

People are considered at higher-than-average risk if they have

  • Had colon polyps removed
  • Relatives who developed the disease
  • Inherited colon cancer syndrome
  • A family history of this syndrome


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