Stool Tests for Colorectal Cancer
A stool test is one of many tests used to look for colorectal cancer. These tests may find cancer early, when treatment works better. Colorectal cancer affects the large
intestine (colon 
) and the
rectum.
There are three kinds of stool tests:
- Fecal occult blood test (FOBT). For this test, you put tiny samples of your stool on a special card or cloth and send it to a lab. The lab uses chemicals to find blood that you can't see with the naked eye. With some test kits, you can add the chemicals yourself at home. FOBT tests don't cost much. This test should be done every year after age 50.
- Fecal immunochemical test (FIT). This is a test that may be easier to do at home than FOBT. There are no drug or food restrictions, and collecting a stool sample may take less effort. But it costs more than FOBT. This test should be done every year after age 50.
- Stool DNA test (sDNA). Instead of looking for blood in the stool, this test looks for abnormal DNA from cancer or polyp cells. Of the three tests, it costs the most. This test should be done every 5 years after age 50.
Blood in the stool may be the only symptom of colorectal cancer, but not all blood in the stool is caused by cancer. Other conditions that can cause blood in the stool include:
- Hemorrhoids. These are enlarged, swollen veins in the anus. Hemorrhoids can form inside the anus (internal hemorrhoids) or outside of the anus (external hemorrhoids).
- Anal fissures. These are thin tears in the tissue that lines the anus (anal sphincter) up into the anal canal.
- Colon polyps. These growths of tissue are attached to the colon and often look like a stem or stalk with a round top.
- Peptic ulcers. These sores form when the digestive juices made in the stomach eat away at the lining of the digestive tract.
- Ulcerative colitis. This type of inflammatory bowel disease (IBD) causes inflammation and sores (ulcers) in the inner lining of the colon and rectum.
- Gastroesophageal reflux disease (GERD). This is the abnormal backflow (reflux) of food, stomach acid, and other digestive juices into the esophagus.
- Crohn's disease. This type of inflammatory bowel disease causes inflammation and ulcers that may affect the deep layers of the lining of the digestive tract.
- Use of aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs).
Stool tests may be used to check for colorectal cancer, but they are never used to diagnose it. Other tests for colorectal cancer include flexible sigmoidoscopy, colonoscopy, and CT scan (virtual colonoscopy).
Which screening test you choose depends on your risk, your preference, and your doctor. Talk to your doctor about what puts you at risk and what test is best for you.
For more information on tests for colorectal cancer, see:
WebMD Medical Reference from Healthwise
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