To verify that red cell inclusions contain iron, it is necessary to use an iron stain, such as Prussian blue. The iron-containing granules are called siderotic granules. Pappenheimer bodies are siderotic granules that are visible on a Wright-stained smear. All Pappenheimer bodies are Prussian blue positive, but not all siderotic granules are visible on Wright-stained smears as Pappenheimer bodies (remember that Wright or Wright-Giemsa stain does not stain the iron, but rather the protein matrix that contains the iron).
A mature erythrocyte containing siderotic granules is referred to as a siderocyte, while an immature (nucleated) erythrocyte containing siderotic granules is known as a sideroblast.
