Storage forms normally comprise approximately 27% of total body iron. Stored iron provides a source of iron when physiologic demand is high, such as in blood loss, pregnancy, and periods of rapid growth.

Storage compounds include ferritin and hemosiderin. Ferritin is a protein-bound, water-soluble, mobilizable storage compound and is the major source of stored iron. Hemosiderin is a water-insoluble form that is less readily available for use.

When the amount of total body iron is relatively low, storage iron consists predominately of ferritin. When iron stores are increased, hemosiderin predominates. Unlike ferritin, hemosiderin stains with the Prussian blue stain (Perls reaction) and may be observed in tissues.