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.¹ 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 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 cells 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 growths can sometimes be removed. Although a sigmoidoscopy does not cover the entire colon, a study has found that when combined with an FOBT, it can detect about 76% of advanced colon polyps or cancers.²
• Colonoscopy. This screening method allows a doctor to inspect the entire colon for polyps and cancer. During a colonoscopy, samples of any growths can be collected (biopsied), and precancerous and cancerous growths sometimes can be removed. Expert groups recommend having the test every 10 years beginning at age 50 for people who are at average risk of colon cancer or whenever another screening test is positive for possible colon polyps or cancer. Screening may begin earlier and be more frequent in people at higher risk for colon polyps and colon cancer.³
• Double-contrast barium enema (DCBE). This exam, also known as a lower gastrointestinal (GI) exam, is an X-ray of the large intestine. A double-contrast barium enema can be used to screen for colon cancer, because it can detect polyps in the entire colon. But a DCBE is not as accurate as a colonoscopy. DCBE also does not allow the doctor to do a biopsy or remove polyps.
• 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.

Screening for colon cancer

Screening for colon cancer with a single test or a combination of tests reduces your chance of having complications and dying from colon cancer. Expert groups recommend routine colon cancer screening for all people older than 50 who are at average risk for colon cancer. These are people who have no family history of colon polyps or colon cancer, have not had colon polyps or colon cancer, and are not having symptoms of colon cancer.

If you are older than 50, screening may lower your risk of dying from colon cancer. Screening options include the following tests.

• Stool tests, such as:
  • A fecal occult blood test (FOBT) every year.
  • A fecal immunochemical test (FIT) every year.
  • A stool DNA test (sDNA). Experts have not yet set guidelines for how often this test should be done.⁴
• Flexible sigmoidoscopy every 5 years.
• Stool test (FBOT or FIT) every year and a flexible sigmoidoscopy every 5 years.
• Double-contrast barium enema (DCBE) every 5 years.
• Colonoscopy every 10 years.
• Computed tomographic colonography (CTC), known as virtual colonoscopy, possibly every 5 years. Experts have not yet set guidelines for how often this test should be done.⁴

The method of screening that you have depends on your personal preferences, your doctor’s preferences, and what the clinic or office you go to is able to do.

Should I have a sigmoidoscopy or a colonoscopy to screen for colorectal cancer?

If you are at increased risk of developing colon cancer, you may need to begin screening earlier or to be tested more often.

If you have a family history of colon cancer, you should begin having tests for the disease either at age 40 or when you are 10 years younger than the age of the youngest case in your immediate family.

If you have a family history of familial adenomatous polyposis (FAP), you should begin screening exams beginning at age 10 or 12.³

If you have a family history of hereditary nonpolyposis colon cancer (HNPCC), you should have a colonoscopy every 1 to 2 years starting at age 20 to 25, or 10 years younger than the age at which the youngest family member who has colorectal cancer was diagnosed, whichever comes first.³

The decisions about when to start and stop screening for colon cancer should be made with your doctor. These decisions will depend on how old you are, your family history, any health problems you may have, and the benefits you can expect from regular screening.

Follow-up testing

If a biopsy of polyps obtained during screening reveals only hyperplastic polyps of any size, routine follow-up screening is all that is needed. These polyps do not become cancerous.

Most doctors agree that if you have had one or more adenomatous polyps removed, you probably need regular follow-up colonoscopy exams every few years.³ This type of polyp is more likely to turn into cancer, but that risk is still very low. How often you need a colonoscopy may depend on the number and size of the polyps, your age, your health, and other risk factors that you may have for polyps. Talk with your doctor about the follow-up testing schedule that is right for you.

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Author:	Monica Rhodes	Last Updated: May 14, 2007
Medical Review:	Kathleen Romito, MD - Family Medicine Peter J. Kahrilas, MD - Gastroenterology
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