Anemia is a group of clinical syndromes that occur when the volume of red blood cells in peripheral blood is lower than normal. Clinically, there are several ways to classify anemia, and the common classifications are: i. According to the hemoglobin concentration, anemia is divided into four degrees, between 90-120 grams is mild anemia, between 60-90 grams is moderate anemia, between 30-60 grams is severe anemia, and less than 30 grams is very severe anemia. Second, according to the morphological size of red blood cells, there are small cell anemia, such as iron deficiency anemia; large cell anemia, such as megaloblastic anemia; and orthocytic anemia, such as aplastic anemia. Third, according to the degree of bone marrow proliferation, it is divided into proliferative anemia and hypoproliferative anemia, among which aplastic anemia is hypoproliferative anemia and the rest of the anemia types are all proliferative anemia.