An iron stain, such as Prussian blue, is necessary to verify that red cell inclusions contain iron. The iron-containing granules are called siderotic granules. Pappenheimer bodies are siderotic granules 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.
A mature erythrocyte containing siderotic granules is called a siderocyte, while an immature (nucleated) erythrocyte containing siderotic granules is known as a sideroblast.