Introduction Inadequate intake of dietary iron Blood loss during the extracorporeal procedure in hemodialysis patients Blood loss from the gastrointestinal tract (bleeding) (Too) frequent diagnostic blood tests Inadequate intestinal iron absorption and inhibition of iron release from macrophages (anemia of chronic disease) Increased iron requirements during therapy with erythropoiesis-stimulating agents (ESAs). In iron deficiency without anemia, reduction in iron storage is not sufficiently large enough to decrease the hemoglobin level. In CKD patients with absolute iron-deficient anemia, however, iron deficit is so severe that it aggravates renal anemia. Iron supplementation is mandatory in the majority of patients with end-stage renal disease (ESRD), particularly in those receiving ESA therapy. Evaluation of iron status 1 2 1 3 4 5 2 6 7 8 9 10 11 12 13 14 8 15 16 Detection of both absolute and functional iron deficiency is important because iron deficiency is the most common cause of hyporesponsiveness to ESAs. In clinical practice, an increased erythropoietic response to iron supplementation is the most widely accepted reference standard of iron-deficient erythropoiesis. For pharmacological therapy of iron deficiency, both oral and parenteral iron preparations are available. Intravenous iron is more effective than oral iron supplementation, at least in CKD patients. Iron is not only a prerequisite for effective erythropoiesis but also an essential element in all living cells. Elemental iron serves as a component of oxygen-carrying molecules and as a cofactor for enzymatic processes. Its redox potential, however, limits the quantity of iron that can be safely harbored within an individual. Oral iron therapy 17 18 19 20 21 22 23 3+ 2+ 2+ 24 25 18 26 Intravenous iron therapy 27 34 1 2 35 1 2 36 37 32 34 38 29 39 2 40 1 41 42 42 43 16 16 44 45 46 3 4 47 48 49 50 51 52 53 Iron and inflammation/infection 54 55 56 55 55 56 55 57 58 58 59 60 61 62 64 64 65 65 Iron and kidney function 37 66 67 68 69 70 2 2 70 71 Iron and oxidative stress 72 70 73 75 75 76 2 77 78 37 59 79 80 79 81 82 82 Vitamin C and iron 83 84 85 86 87 88 89 90 91 92 93 99 100 Iron therapy after kidney transplantation 101 104 105 106 107 108 109 Conclusions 110 110