Trivalent iron (Fe+++) can be demonstrated by the Prussian blue stain. The tissue iron forms together with the yellowish potassium ferrocyanide (K4[Fe++(CN)6]) a dark blue pigment (Fe+++4[Fe++(CN)6]3).
4 Fe+++Cl3 + 3 K4[Fe++(CN)6] -> Fe+++4[Fe++(CN)6]3 + 12 KCl
Iron in hemosiderin and cellular ferritin stains blue. Cellular components become red in the counter-staining. Most iron in the bone marrow is stored as hemosiderin in macrophages (in smaller amounts also in reticulum and in endothelial cells). The iron content of the bone marrow can be determined by iron staining, which is a good parameter of the body's iron content. In normal iron content, many coarse blue clods of macrophage iron are spread throughout the bone marrow. In decreased iron storage, these clods are rare or missing in depleted iron storage. In increased iron storage, hemosiderin clods are densely bedded.
Sideroblasts (left image) are physiologically found in the bone marrow. Few iron granules are diffusely spread over the cytoplasm. Ringed sideroblasts (right image) are always pathological and a sign of a sideroachrestic disorder. In ringed sideroblasts, the iron granules are arranged around the nucleus. By definition, a ringed sideroblast contains 5 or more granules that encompass at least one third of the nucleus.
In the blood, iron granules can be demonstrated in erythrocytes. These are called siderocytes. These iron granules correspond to the Pappenheimer bodies in the May-Gruenwald-Giemsa stain. Siderocytes are increased after splenectomy and in iron utilization disorders.
A bone marrow procedure is not necessary for the clinical evaluation of iron deficiency anemia. Serum parameters of the iron metabolism, especially ferritin, are better suited , simpler, and cheaper. However, if an aspiration was performed, the demonstration of missing iron stores is diagnostic.
The detection of ringed sideroblasts is of decisive importance for the diagnosis of sideroachrestic anemia, especially in myelodysplastic syndromes.