<prompt> Best indicator of iron deficiencySerum ironSerum ferritinTIBCTransferrin  <response>: In iron deficiency anemia, ferritin content is reduced. When iron is given in anemia, the apoferritin production is induced within a few hours. vii. Estimation of ferritin in chronic kidney disease CKD is of prognostic significance since ferritin level less than 100 microgramdl indicates iron deficiency. Transferrin saturation less than 20 and ferritin between 100 and 200 microgramdl is suggestive of functional deficiency. In order to treat the anemia in CKD, the iron stores should be adequate and this is denoted by serial ferritin estimations in a patient on treatment to check the efficacy of treatment with recombinant erythropoietinRef: DM Vasudevan, page no: 425 