Hemosiderin is a hemoglobin-derived pigment, golden yellow or brownish-yellow particles, because of its iron content and golden color, so it is called iron-containing hemosiderin, when the red blood cells are phagocytosed by macrophages, under the action of lysosomal enzymes, hemoglobin is broken down into iron-containing orange blood plasma and iron-containing iron-containing hemosiderin.Perls Prussian blue reaction (Prussian) is also known as iron-containing hemosiderin staining, that is, after potassium ferricyanide and dilute acid treatment can produce blue color. Perls Prussian blue reaction is also known as ferrous hemoflavin staining, that is, after treatment with potassium ferricyanide and dilute acid can produce a blue color, commonly found in phagocytes or mesenchymal stroma, the staining principle lies in the separation of trivalent iron ions from proteins by dilute hydrochloric acid by a solution of potassium ferricyanide, and the reaction between the trivalent iron and potassium ferricyanide, resulting in the production of an insoluble blue compound, i.e., ferrous cyanide of the trivalent iron.

Prussian blue staining is used to show various hemorrhagic lesions in local tissues, which are commonly found in phagocytes, and can well distinguish ferric hemoflavin from other pigments, the stain is stable, can be stored for a long time, is not easy to produce precipitation, has a wide range of applications, and can be restained, and the restaining solution of this stain uses eosin.