Ferritin test is used to assess the levels of iron stored in your body. Within cells, iron is stored bound to protein, forming complexes called ferritin and haemosiderin. Ferritin is the main storage complex and is present mostly in the liver, but also in the bone marrow, spleen, and muscles. Small amounts of ferritin also circulate in the blood. The ferritin concentration within the blood stream reflects the amount of iron stored in your body.