HGB means hemoglobin, and low hemoglobin is anemia, a clinical syndrome that occurs in patients with insufficient red blood cell volume due to various causes. Anemia is a symptom that causes anemia in three ways: First, insufficient red blood cell production: insufficient red blood cell production is the most common cause of anemia, and common diseases include aplastic anemia, pure red blood cell aplastic anemia, acute leukemia, myelodysplastic syndrome; and anemia caused by lack of hematopoietic materials, such as iron deficiency anemia and macrocytic anemia. Second, excessive destruction of red blood cells: anemia caused by excessive destruction of red blood cells, the most common ones are hemolytic anemia, serotonin and thalassemia. Third, there is loss of red blood cells. It is bleeding disorders caused by various reasons, such as bleeding hemorrhoids, bleeding peptic ulcers, and bleeding gastrointestinal tumors.