Iron storage and recycling Iron not used for erythropoiesis is transferred by transferrin to the storage pool; iron is stored in 2 forms: Ferritin Hemosiderin The most important storage form is ferritin (a heterogeneous group of proteins surrounding an iron core), which is a soluble and active storage fraction located in the liver (in hepatocytes), bone marrow, and spleen (in macrophages); in red blood cells (RBCs); and in serum.