Low hemoglobin concentration of red blood cells may be caused by malnutrition, excessive blood loss and abnormal hematopoietic function. 1. Malnutrition: If the intake of iron is too low, vitamin B group elements are insufficient, it may cause hemoglobin insufficiency, the number of red blood cells decreases, resulting in megaloblastic anemia, iron-deficiency anemia and other diseases, and low red blood cell hemoglobin concentration occurs. 2. Excessive blood loss: when the human body suffers from bleeding, it may cause a decrease in the number of red blood cells in the body and a decrease in the concentration of hemoglobin, which mainly includes diseases such as bleeding from peptic ulcers, severe traumas, excessive menstruation, and chronic bleeding from intestines. 3. Abnormal hematopoietic function: As red blood cells are generated in the bone marrow, they enter the blood circulation after maturation. When hematopoiesis is abnormal, it will easily cause low hemoglobin concentration of red blood cells. Commonly found in aplastic anemia, acute leukemia and so on. Low red blood cell hemoglobin concentration should be timely to the hospital, after clarifying the cause of anemia, under the guidance of physicians to give appropriate treatment.