Occult blood in the stool is considered to be the result of eating animal blood or gastrointestinal bleeding, as follows: First, it may be related to the consumption of animal blood, etc. Second, gastrointestinal bleeding: if gastrointestinal bleeding occurs, if the daily bleeding amount of adults > 5mL, fecal occult blood test can appear positive, if the daily bleeding amount exceeds 50mL, it can be shown as black stool or tarry stool. Blood accumulation in the stomach >250mL can cause vomiting of blood. When the amount of bleeding at one time is <400mL, it can be supplemented by tissue fluid and spleen bleeding due to mild blood volume reduction and mostly does not cause symptoms, but when the amount of bleeding is >400mL, symptoms such as dizziness, palpitations and general weakness will occur. After the appearance of positive fecal occult blood, gastrointestinal bleeding can be excluded mainly by identifying the following three causes, as follows: First, hemoptysis is caused by the respiratory organs below the larynx and tracheobronchial and pulmonary tissues, and is discharged through coughing and swallowing from the mouth to the stool. Second, bleeding from the mouth, nose, throat, and pharynx is generally bright red in color and is not accompanied by gastrointestinal symptoms such as nausea, vomiting, abdominal distention, and irritability. Third, black stools caused by food and drugs, including animal blood, charcoal powder, iron, bismuth, etc. can cause black stools, but not always with positive occult blood, so attention should be paid to identification and differentiation in order to guide further treatment.