Colon Cancer Screening (cont.)
Dennis Lee, MD
Dr. Lee was born in Shanghai, China, and received his college and medical training in the United States. He is fluent in English and three Chinese dialects. He graduated with chemistry departmental honors from Harvey Mudd College. He was appointed president of AOA society at UCLA School of Medicine. He underwent internal medicine residency and gastroenterology fellowship training at Cedars Sinai Medical Center.
In this Article
- Introduction to colon cancer screening and surveillance
- Screening recommendations for individuals with average risk of colon cancer
- Fecal occult blood tests
- Flexible sigmoidoscopy
- Screening colonoscopy
- Virtual colonoscopy
- Air contrast (double contrast) barium enema
- Surveillance recommendations for individuals with higher-than-average risk of colon cancer
- Patients with history of colon polyps
- Patients with history of colorectal cancer
- Patients with ulcerative colitis
- Family history of colorectal cancer
- What are hereditary colon cancer syndromes?
- Who should consider genetic counseling and testing and how is it conducted?
- Summary of colon cancer screening
Screening recommendations for individuals with average risk of colon cancer
The life-time risk for an adult American to develop colorectal cancer is approximately 6%. Fecal occult blood tests and flexible sigmoidoscopic examinations are the recommended screening tests for these individuals at average risk for developing colorectal cancer. These tests are designed to detect and to prompt removal of precancerous polyps and identify early cancers in order to decrease mortality from colorectal cancer. Fecal occult blood testing and sigmoidoscopy are affordable, easy to perform, and comfortable for healthy individuals.
Fecal occult blood tests
Fecal occult blood tests are chemical tests that are performed on samples of stool to detect the presence of "occult" blood (amounts of blood that are so small that they cannot be seen with the naked eye). These tests usually are begun at age 40 and then are repeated annually along with a digital rectal examination that is performed by a doctor. The use of fecal occult blood tests is based on observations that slow bleeding from colon polyps or cancers can cause small amounts of blood to mix with the colonic contents. (This sometimes can lead to an iron deficiency anemia.) Since the small amounts of blood are not visible to the naked eye, sensitive chemical tests are needed to detect the traces of blood in the stool.
Fecal occult blood testing consists of checking for occult blood in 3 stool specimens collected on special cards at home. To properly prepare for collecting the specimens, individuals are asked to abstain (for 3-5 days before stool collections begin) from certain foods, medications and vitamins that can interfere with the accuracy of the test. These include certain meats, vitamins (especially vitamin C), iron, aspirin, and other antiinflammatory medicines (NSAIDs) such as ibuprofen that are used in treating arthritis and other painful inflammatory conditions.
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A more recent form of this test called a Fecal Immunochemical, or FIT test, does not require the same precautions and restrictions and is probably even more sensitive than the older chemical or guiac based tests for colorectal cancer. It tests 2 stools collected on 2 consecutive days.The FIT test is more expensive than the older test, and your doctor will know if insurance will cover it.
An individual whose stool specimen tests positive for occult blood then undergoes a colonoscopic examination of the entire colon to look for polyps, cancers, or other conditions that cause bleeding (such as abnormal blood vessels, diverticuli, or colitis). The majority (greater than 90%) of the polyps detected at colonoscopy can be removed painlessly and safely during the colonoscopic examination. Polyps so removed are examined later under the microscope by a pathologist to determine if they are precancerous. Individuals with precancerous polyps have a higher than average risk for developing colon cancer, and are advised to return for periodic surveillance colonoscopies (see below). Colon cancers that are detected at colonoscopy usually are removed surgically though under certain circumstances they may be removed at colonoscopy. Precancerous polyps that are too large or technically not possible to remove during colonoscopy also are removed surgically. Several studies have shown that fecal occult blood testing can reduce death rates (mortality) from colorectal cancer by 30% to 40%.
If no colonic abnormalities are found in an individual whose stool contains occult blood, consideration then is given to examining the stomach and the small intestine as sources of bleeding.
A DNA test on stool has also been developed as a screening tool. Preliminary testing suggests it may be even more sensitive than FIT testing though the larger number of false positive tests mean it may not be as specific as FIT. It is called Cologuard and is was not FDA approved as of April, 2014.
Next: Flexible sigmoidoscopy
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