Hemolytic anemia is anemia that occurs when the destruction of red blood cells is accelerated and the hematopoietic function of the bone marrow is insufficient to compensate. The average survival time of normal red blood cells is about 120 days, while the survival time of red blood cells in hemolytic anemia is often shortened to less than 15 to 20 days, and the shortest is only a few days. Premature destruction of red blood cells can occur outside or inside blood vessels. Extravascular hemolysis means that red blood cells are destroyed and eliminated after being phagocytosed by macrophages in the spleen and liver. Intravascular hemolysis means that red blood cells rupture directly in the blood circulation and hemoglobin is released into the plasma. When hemolysis increases, if the hematopoietic function of the bone marrow can compensate, anemia may not occur. This situation is called compensated hemolytic disease. However, if the hematopoietic function of the bone marrow has been accelerated, but is still slower than the rate of red blood cell destruction, hemolytic anemia will occur.