The clinical significance of hemoglobin concentration is to determine the severity of anemia, and its increase or decrease suggests changes in physiological activity of the body or certain diseases. Depending on the hemoglobin concentration, anemia can be classified as mild anemia, moderate anemia, severe anemia, and very severe anemia. In mild anemia, the hemoglobin concentration is ≥90g/L; in moderate anemia, the hemoglobin concentration is 61-90g/L; in severe anemia, the hemoglobin is 31-60g/L; and in very severe anemia the hemoglobin concentration is ≤30g/L. Increased hemoglobin concentration: relative elevation such as massive sweating, vomiting and other dehydration caused by concentration; absolute elevation such as congenital heart disease, pulmonary heart disease, erythrocytosis and so on. Decrease in hemoglobin concentration: can be seen in physiological decrease such as rapid growth, pregnancy, the elderly, etc.; pathological decrease such as iron deficiency anemia, aplastic anemia, hereditary spherocytosis, etc.. If abnormalities are found in the examination and physiological causes are excluded, the causes should be further investigated and diagnosed clearly, and targeted treatment or therapy should be given.