Extracellular iron refers to the bone marrow particles in the iron-containing hemoflavin, the normal range of extracellular iron is “+” to “++”, so the positive extracellular iron is normal, while the extracellular iron decreased and elevated is suggestive of some diseases. 1. Decrease: seen in iron deficiency anemia. In iron deficiency anemia, extracellular iron in bone marrow is obviously reduced or even disappeared, and iron granulocytes are reduced. After iron treatment, extracellular iron increases. Iron granule staining can be used as a method to diagnose iron deficiency anemia and guide iron therapy. 2. Elevated: seen in Fe-granulocyte anemia, myelodysplastic syndrome (Fe-granulocyte refractory anemia) and so on. In addition, it is also seen in hemolytic anemia, nutritional megaloblastic anemia, aplastic anemia and leukemia, infection, cirrhosis of the liver, chronic nephritis, uremia, multiple blood transfusions, hemochromatosis and so on. Extracellular iron staining is one of the important tests for clinical diagnosis of anemia-related diseases, and further consultation and treatment are recommended when abnormalities are detected.