Chemical test of stool for blood, especially blood that is not visible to the naked eye (occult blood). If the test is positive, the stool is classified as guiac-positive. Testing stool for occult blood is a routine part of the physical exam in patients over 40 years of age as a screen for colon cancer. A newer kind of stool blood test kit, known as a fecal immunochemical test (FIT), detects a specific portion of a human blood protein. This test is done essentially the same way as conventional guiac test, but it is more specific and reduces the number of false-positive results. Vitamins (e.g., vitamin C) or foods (e.g., red meat) do not affect the FIT.
A test performed on feces or urine to detect occult blood in the intestinal or urinary tract. Guiac, a wood resin, is the reagent used in the laboratory procedure.