The main use of this test is as a screen for early colon cancer. Blood in the stool can be the only symptom of early cancer. If the cancer is detected early, the chance increases that it will be curable. This test is not diagnostic for cancer; other follow-up procedures would need to be done to find the source of the bleeding as the blood may also indicate other gastrointestinal problems. A secondary use for this test is to look for a cause of anemia, such as blood loss from a bleeding ulcer. You may want to order this test if you have symptoms and signs of anemia, such as fatigue or a low hemoglobin and hematocrit, and/or unusually dark stools. Patient shouldn't receive vitamin C (ascorbic acid) for three days prior to occult blood testing by guaiac. A high bulk, red meat free diet with restriction of peroxidase-rich vegetables is recommended for 72 hours prior to guaiac testing, and during testing, to decrease the incidence of false-positives. In more than half of healthy subjects, therapeutic iron causes false-positives with guaiac tests.
