The criteria for grading the degree of anemia is the hemoglobin concentration. Anemia is a syndrome in which the red blood cell count and hemoglobin concentration in the peripheral blood of the human body are lower than the lower limit of normal, resulting in the body’s inability to transport sufficient oxygen to the tissues and organs throughout the body. The lower limit of normal hemoglobin value is 120g/L for adult males, 110g/L for adult females, and 144g/L for newborns, with different values for children at different ages. Clinically, anemia is usually classified into mild anemia, moderate anemia, severe anemia and very severe anemia based on hemoglobin concentration. Mild anemia is defined as hemoglobin concentration greater than or equal to 90g/L and less than the lower limit of normal value, moderate anemia is defined as hemoglobin concentration greater than or equal to 60g/L and less than 90g/L, severe anemia is defined as hemoglobin concentration greater than or equal to 30g/L and less than 60g/L, and extremely severe anemia is defined as hemoglobin concentration less than 30g/L. It should be noted that the lower limit of normal hemoglobin value varies from one medical institution to another, and the severity of anemia should be diagnosed by a doctor.