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Colorectal Cancer Health Center

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Colon Polyps - Exams and Tests

Unless colon polyps are large and cause bleeding or pain, the only way to know if you have polyps is to have one or more tests that explore the inside surface of your colon.

Several tests can be used to detect colon polyps. Two of these exams, flexible sigmoidoscopy and colonoscopy, also can be used to collect tissue samples (called a biopsy) or to remove colon polyps. All the tests may be used to screen for colon polyps and colon cancer and as follow-up tests after colon polyps have been removed. There are two basic types of tests-stool tests and tests that look inside your body.

Stool tests

  • Fecal occult blood test (FOBT). A fecal occult blood test (FOBT) is done to look for microscopic amounts of blood in stool. FOBT is a simple, low-cost screening tool for colon polyps or colon cancer. FOBT has been shown in studies to reduce the number of deaths from colon cancer. By itself, an FOBT is not evidence of colon polyps or colon cancer. And a negative FOBT (no blood found) does not mean that you do not have polyps or colorectal cancer. If a fecal occult blood test is positive for blood in the stool, it is important to have a colonoscopy to help your doctor find the source of the blood and remove polyps if they are found.
  • Fecal immunochemical test (FIT). This test also looks for blood in the stool, but it is more specific than the FOBT. There aren't as many restrictions on what you can eat before having this test, and fewer stool samples are required. If the test is positive for blood in the stool, you may need to have a colonoscopy.
  • Stool DNA test (sDNA). This test checks for changes to the cells in the colon by looking at DNA in the stool. Certain kinds of changes in cell DNA happen when you have cancer. Like the other stool tests, if your test is positive, you may need to have a colonoscopy.

Tests that look inside your body

  • Flexible sigmoidoscopy.Flexible sigmoidoscopy allows the doctor to look at the lower third of the colon. During a sigmoidoscopy exam, samples of any growths can be collected (biopsied). And precancerous and cancerous polyps can sometimes be removed.
  • Colonoscopy. This screening method lets a doctor inspect the entire colon for polyps and cancer. During a colonoscopy, samples of any growths can be collected (biopsied). And precancerous and cancerous polyps usually can be removed.
  • Computed tomographic colonography (CTC). This test is also called virtual colonoscopy. A computer and X-rays make a detailed picture of the colon to help the doctor look for polyps. If this test finds polyps, you may need to have a colonoscopy.
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