This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: nutrition and digestion, Subject name: Biochemistry
Best indicator of iron deficiency 
Select and explain. 
A. Serum iron, B. Serum ferritin, C. TIBC, D. Transferrin
B: Serum ferritin
Answer: B: Serum ferritin 
Explanation: 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 microgram/dl indicates iron deficiency. Transferrin saturation less than 20% and ferritin between 100 and 200 microgram/dl 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