A positive occult blood test, which mostly indicates a small amount of bleeding, can be divided into a positive urine occult blood test and a positive stool occult blood test. A positive urine occult blood test is defined as more than 10 red blood cells per milliliter of urine and is commonly associated with diseases such as urinary stones, urinary tuberculosis, and urinary tumors. A positive fecal occult blood test is defined as a small amount of bleeding from the gastrointestinal tract, with red blood cells destroyed by digestion and no abnormal change in the appearance of the stool, and bleeding cannot be confirmed by the naked eye or microscopy. There are two commonly used methods for a positive fecal occult blood test, the chemical method and the immunoassay method. The chemical method is simple and easy to use, but lacks specificity, for example, the occult blood test can be positive after oral intake or ingestion of blood from animals. The immunoassay method is sensitive and specific, and is not affected by other animal blood factors, so there is no need to control the diet. The clinical significance of a positive fecal occult blood test is very important and can be useful in the differential diagnosis of gastrointestinal bleeding. Peptic ulcers have a positive rate of 40%-70% and are intermittently positive, while malignant tumors of the gastrointestinal tract, such as gastric and colon cancers, have a positive rate of up to 95% and are persistently positive. When a positive occult blood test is found, you should consult a hospital promptly and let the doctor improve abdominal CT, colonoscopy and other tests to clarify the diagnosis.