Occult blood usually includes urinary occult blood and fecal occult blood, the common causes are as follows: 1. Urinary occult blood: including glomerulonephritis, tonsillitis, women’s menstrual blood or trauma and other causes of urine contamination, strenuous exercise muscle strain, resulting in myoglobinuria caused by muscle cell damage, and various causes of intravascular hemolysis caused by hemoglobinuria, etc., and taking rifampin, phenytoin sodium and other drugs and their metabolites can cause urinary occult blood, and the consumption of foods such as beets, red heart dragon fruit and chili peppers can also lead to positive urinary occult blood. Therefore, when a patient has positive urinary occult blood, it is necessary to further combine the count of red blood cells under high magnification in the urine sediment to determine whether the patient has real meaningful hematuria; 2. Fecal occult blood: usually seen in patients with organic lesions of the gastrointestinal tract, more common are gastric ulcer, gastric cancer, ulcerative colitis, colon polyps, rectal polyps, proctitis, colorectal cancer and so on. Usually the daily bleeding volume is relatively small, usually around 5mL, the color of the stool is normal to the naked eye and no blood can be seen, but the blood components can be checked by chemical tests, and three consecutive tests are needed to improve the credibility of the diagnosis.