March is National Colorectal Cancer Awareness Month, and early detection is vitally important. Screening is the process of looking for cancer in people who have no symptoms of the disease. Several different tests can be used to screen for colorectal cancers. These tests can be divided into two broad groups:
• Tests that can find both colorectal polyps and cancer: These tests look at the structure of the colon itself to find any abnormal areas. This is done either with a scope inserted into the rectum or with special imaging (x-ray) tests. Polyps found before they become cancerous can be removed, so these tests may prevent colorectal cancer. Because of this, these tests are preferred if you are willing to have them.
• Tests that mainly find cancer: These involve testing the stool (feces) for signs that cancer may be present. These tests are less invasive and easier to have done, but they are less likely to detect polyps.
Tests that can find both colorectal polyps and cancer
• Flexible sigmoidoscopy
During this test, the doctor looks at part of the colon and rectum with a sigmoidoscope - a flexible, lighted tube about the thickness of a finger with a small video camera on the end. It is inserted through the rectum and into the lower part of the colon. Images from the scope are viewed on a display monitor.
Using the sigmoidoscope, your doctor can view the inside of the rectum and part of the colon to detect (and possibly remove) any abnormality. Because the sigmoidoscope is only 60 centimeters (about 2 feet) long, the doctor is able to see the entire rectum but less than half of the colon with this procedure.
For this test, the doctor looks at the entire length of the colon and rectum with a colonoscope, which is basically a longer version of a sigmoidoscope. It is inserted through the rectum into the colon. The colonoscope has a video camera on the end that is connected to a display monitor so the doctor can see and closely examine the inside of the colon. Special instruments can be passed through the colonoscope to remove (biopsy) any suspicious looking areas such as polyps, if needed.
• Double-contrast barium enema
The double-contrast barium enema (DCBE) is also called an air-contrast barium enema or a barium enema with air contrast. It may also be referred to as a lower GI series. It is basically a type of x-ray test. Barium sulfate, which is a chalky liquid, and air are used to outline the inner part of the colon and rectum to look for abnormal areas on x-rays. If suspicious areas are seen on this test, a colonoscopy will be needed to explore them further.
• CT colonography (virtual colonoscopy)
This test is an advanced type of computed tomography (CT or CAT) scan of the colon and rectum. A CT scan is an x-ray test that produces detailed cross-sectional images of your body. Instead of taking one picture, like a regular x-ray, a CT scanner takes many pictures as it rotates around you while you lie on a table. A computer then combines these pictures into images of slices of the part of your body being studied. For CT colonography, special computer programs create both two-dimensional x-ray pictures and a three-dimensional “fly-through” view of the inside of the colon and rectum, which allows the doctor to look for polyps or cancer.
This test may be especially useful for some people who can’t have or don’t want to have more invasive tests such as colonoscopy. It can be done fairly quickly and does not require sedation. But even though this test is not invasive like colonoscopy, it still requires the same type of bowel preparation and uses a tube placed in the rectum (similar to the tube used for barium enema) to fill the colon with air. Another possible drawback is that if polyps or other suspicious areas are seen on this test, a colonoscopy will still probably be needed to remove them or to explore them fully.
Tests that mainly find colorectal cancer
These tests look at the stool for signs of cancer. Most people find these tests to be easier because they are not invasive and can often be done at home, but these tests aren’t as good as the ones described above for finding polyps. A positive result on one of these screening tests will likely require a more invasive test such as colonoscopy.
• Fecal occult blood test
The fecal occult blood test (FOBT) is used to find occult (hidden) blood in feces. The idea behind this test is that blood vessels at the surface of larger colorectal polyps or cancers are often fragile and easily damaged by the passage of feces. The damaged vessels usually release a small amount of blood into the feces, but only rarely is there enough bleeding to be visible in the stool.
The FOBT detects blood in the stool through a chemical reaction. This test cannot tell whether the blood is from the colon or from other parts of the digestive tract (such as the stomach). If this test is positive, a colonoscopy is needed to see if there is a cancer, polyp, or other cause of bleeding such as ulcers, hemorrhoids, diverticulosis (tiny pouches that form at weak spots in the colon wall), or inflammatory bowel disease (colitis).
This screening test is done with a kit that you can use in the privacy of your own home. An FOBT done during a digital rectal exam in the doctor’s office is not sufficient for screening. In order to be beneficial, the test must be repeated every year.
People having this test will receive a kit with instructions from their doctor’s office or clinic. The kit will explain how to take a stool or feces sample at home (usually specimens from three consecutive bowel movements that are smeared onto small squares of paper). The kit should then be returned to the doctor’s office or medical lab (usually within two weeks) for testing.
If this test finds blood, a colonoscopy will be needed to look for the source. It is not sufficient to simply repeat the FOBT or follow up with other types of tests.
• Fecal immunochemical test
The fecal immunochemical test (FIT), also called an immunochemical fecal occult blood test (iFOBT), is a newer kind of test that also detects occult (hidden) blood in the stool. This test reacts to part of the human hemoglobin protein, which is found on red blood cells.
The FIT is done essentially the same way as the FOBT, but some people may find it easier to use because there are no drug or dietary restrictions (vitamins or foods do not affect the FIT) and sample collection may take less effort. This test is also less likely to react to bleeding from parts of the upper digestive tract, such as the stomach.
Like the FOBT, the FIT may not detect a tumor that is not bleeding, so multiple stool samples should be tested. And if the results are positive for hidden blood, a colonoscopy is required to investigate further. In order to be beneficial, the test must be repeated every year.
Kim Griffin, RN, nurse manager of the Ambulatory Care Unit at Oconee Regional Medical Center, says in addition to regular screenings, the following tips can help decrease the risk of colon cancer. Start with one healthy behavior and build on that.
• Eat more fresh fruits and vegetables.
• Keep your weight within the range recommended by your health care provider.
• Exercise every day.
• Don’t smoke and limit your alcohol to no more than two drinks a day.
• Limit red meat to no more than a few times a week.
Source: American Cancer Society