Low hemoglobin is present with various kinds of anemia, such as aplastic anemia, iron deficiency anemia, iron granulocytic anemia, megaloblastic anemia, hemolytic anemia, thalassemia, etc. If hemoglobin is too low and there is a large amount of blood loss, consider the possibility of various types of hemorrhage, such as acute gastrointestinal bleeding, chronic blood loss due to ulcers, traumatic hemorrhage, surgical hemorrhage, and leukemia, bleeding due to postpartum and post-chemotherapy. The normal value of hemoglobin is 120-160g/L for men and 110-150g/L for women. Less than 90g/L is mild anemia, 60-90g/L is moderate anemia, less than 30-60g/L is severe anemia, and less than 30g/L is very severe anemia.