Occult blood includes occult blood in the urine and occult blood in the stool, which are two systems of disease. Urinary occult blood is mainly seen in diseases of the urinary system, including kidney stones, ureteral stones, bladder stones, urethral stones, and also tumors related to the urinary system, which can also cause occult blood. Occult blood in the stool refers to bleeding from the gastrointestinal tract, and it is a small amount and can be seen in many kinds of diseases. The upper gastrointestinal tract, including esophageal diseases, such as esophagitis and esophageal cancer. There are also stomach-related diseases, including erosive gastritis, hemorrhagic gastritis, drug-induced gastritis, gastric ulcer, and gastric cancer. Duodenal diseases, mainly duodenal bulb ulcers and duodenal descending ulcers, can cause occult blood. There are also diseases of the middle gastrointestinal tract, mainly small intestinal diseases, which are less common, including small intestinal mesenchymal tumors, and small intestinal tumors. Finally, there are lower gastrointestinal diseases, mainly in the large intestine and rectum, and lower gastrointestinal diseases are mainly colorectal cancer and rectal cancer are more common. In addition, including ischemic enteropathy, ulcerative colitis, Crohn’s disease, and drug enteritis, intestinal tuberculosis. Finally, positive fecal occult blood is also very common in hemorrhoids.