Colon and Rectal Cancers - Diagnosis

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Digital Rectal Examination (DRE)

The digital rectal examination is used to detect tumors in the rectum, lower intestine, and prostate gland. The doctor inserts a lubricated-gloved finger into the patient's rectum and feels for lumps or other abnormalities. The exam is quick and painless but embarrassing for some. Fewer than 10% of colon cancers develop within the region that can be evaluated by a DRE, so it is not useful as a sole screening test.

Fecal Occult Blood Test (FOBT)

Blood in bowel movements is not always visible, in which case it is called occult (hidden) blood. Fecal occult blood tests (FOBTs) are used to detect this hidden blood. The most common FOBT method is called the guaiac-based test. The patient is asked to supply up to six stool specimens in a specially prepared package. A small quantity of feces is smeared on specially treated paper, which reacts to hydrogen peroxide. If blood is present, the paper turns blue.

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Accuracy. FOBTs can miss more than 75% of advanced cancers. Nevertheless, large studies have indicated that this simple test, performed annually, saves lives and may reduce the risk of dying from colon cancer by 15 - 33%. The following factors may affect its accuracy:

• The levels of iron in the blood can affects results. Patients should not take iron supplements or eat red meats several days before the test.
• Certain raw fruits and vegetables that contain the chemical peroxidase (cauliflower, horseradish, radishes, melons, and turnips) can cause a positive test reaction even if no blood is present.
• Aspirin and NSAIDs are anticoagulants that can cause minor bleeding. They should not be taken for a week before the test. However, a 2005 study suggested that the prescription anticoagulant warfarin does not affect FOBT results.
• Vitamin C and foods rich in this vitamin may cause a false negative reaction and should be avoided a few days before the test.
• Bleeding from other causes, such as menstruation, hemorrhoids, gingivitis, or urinary infections, can produce blood in the stools and affect results.