The main use of the FOBT is to screen for early colon cancer. Blood in the stool may be the only symptom of early cancer. If the cancer is detected before it metastasizes (spreads to other areas), the chance that it will be curable is increased. The FOBT is not diagnostic for cancer; other follow-up procedures would need to be done to find the source of the bleeding because the blood may also indicate other gastrointestinal problems.

Special Note: What to avoid prior to testing: Patient should not receive vitamin C(absorbic acid for 3 days prior to occult blood testing by guaiac(a leuko-dye). A high bulk, red meat free diet with restriction of peroxidase-rich vegetables(turnips, horseradish, artichokes, mushrooms, radishes, broccoli, bean sprouts, cauliflower, oranges, bananas, canteloupes, grapes), has been recommended for 72 hours prior to guaiac testing, and during testing, to decrease the incidence of false-positives. Therapeutic iron causes false-positives with guaiac tests in over half of healthy people.