Tests used to screen for Colorectal Cancer

The tests used to screen for colorectal cancer are described below:

Colonoscopy. This test allows the doctor to look inside the entire rectum and colon while a patient is sedated. A flexible, lighted tube called a colonoscope is inserted into the rectum and the entire colon to look for polyps or cancer. During this procedure, a doctor can remove polyps or other tissue for examination (see biopsy in theDiagnosis section). This is the only screening test that allows the removal of polyps, which can also prevent colorectal cancer.

Computed tomography (CT or CAT) colonography. CT colonography, sometimes called virtual colonoscopy, is a screening method being studied in some centers. It requires interpretation by a skilled radiologist, a doctor who specializes in obtaining and interpreting medical images, to be used to the best advantage. However, it may be an alternative for people who cannot have a standard colonoscopy due to the risk of anesthesia, which is medication to block the awareness of pain, or if a person has a blockage in the colon that prevents a full examination.

Sigmoidoscopy. A sigmoidoscope is a flexible, lighted tube, and it is inserted into the rectum and lower colon to check for polyps, cancer, and other abnormalities. During this procedure, a doctor can remove polyps or other tissue for later examination. The doctor cannot check the upper part of the colon, the ascending and transverse colon, with this test. If polyps or cancer is found using this test, a colonoscopy to view the entire colon is recommended.

Fecal occult blood test (FOBT). This is a test used to find blood in the feces, or stool, which can be a sign of polyps or cancer. A positive FOBT test, meaning that blood is found in the feces, can be from causes other than a colon polyp or cancer, including bleeding in the stomach or upper GI tract and even ingestion of rare meat or other foods. There are two types of tests: guaiac and immunochemical. Polyps and cancers do not bleed continually, so the FOBT must be done on several stool samples each year and should be repeated yearly. Even then, the reduction in deaths from colorectal cancer is fairly small at around 30% if done yearly and 18% if done every other year.

Double contrast barium enema (DCBE). For patients who cannot have a colonoscopy, an enema containing barium is given, which helps the outline of the colon and rectum stand out on x-rays. A series of x-rays is then taken of the colon and rectum. In general practice, most doctors would recommend other screening tests because a barium enema is less likely to detect precancerous polyps than a colonoscopy, sigmoidoscopy, or CT colonography.

Stool DNA tests. This test analyzes the DNA from a person’s stool sample to look for cancer. It uses changes in the DNA that occur in polyps and cancers to determine whether a colonoscopy should be done.

Screening Recommendations

Different organizations have made different recommendations for colorectal cancer screening. Two sets of recommendations are described below. Talk with your doctor about the best test and time between tests based on your health history and personal cancer risk.

The following tests detect both polyps and cancer:

• Flexible sigmoidoscopy, every five years
• Colonoscopy, every 10 years
• DCBE, every five years
• CT colonography, every five years

These tests primarily detect cancer:

• Guaiac-based FOBT, every year
• Fecal immunochemical test, every year
• Stool DNA test, as often as your doctor recommends
  
  
  
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