Positive fecal occult blood indicates the presence of gastrointestinal bleeding, because after the gastrointestinal bleeding, the reaction of gastric acid makes the stool black to the naked eye or the amount of bleeding is smaller. Only if the amount of gastrointestinal bleeding exceeds 50 ml will a black stool be seen in the naked eye. If the amount is between 5 and 50 ml, only laboratory tests will be able to reflect the presence of GI bleeding, i.e., only through routine occult blood in the stool. Therefore, it is a very sensitive indicator for the diagnosis of gastrointestinal bleeding and should be consulted as soon as possible to consider the presence of gastrointestinal peptic ulcers, intestinal polyps and colonic tumors, inflammation and other gastrointestinal bleeding, all of which will be reflected by the stool occult blood test.