When the amount of gastrointestinal bleeding is less than 50 ml, there is no blood in the stool, which can only be detected by occult blood test, which is called fecal occult blood test positive (also known as occult blood or occult blood positive). Feces can only be positive if they contain more than 5 ml of blood. Its positive degree is as weak as blood; There is a lot of blood and a strong positive reaction. The masculine gender is represented by "+","++"and "++". Positive changes are common in active ulcer, gastric cancer, colon cancer, hookworm disease and so on. Because taking iron, eating animal blood, animal liver, lean meat and a lot of green vegetables can also be positive, it is more accurate to check the fecal occult blood test only after fasting these foods for 3 days. Positive fecal occult blood test is common in active stage of ulcer. If it turns negative after treatment, it means that the ulcer has improved steadily. If the continuous positive rate exceeds 1 month, or it does not turn negative after treatment, gastric cancer and colon cancer should be suspected and further diagnosed. Those with hematemesis and melena should be hospitalized for examination and treatment. Those who have a positive fecal occult blood test can go to the clinic for further examination, and then be treated after a clear diagnosis.