This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood, Subject name: Medicine
Best marker of iron deficiency anemia is? 
Select and explain. 
A. Serum iron, B. Serum ferritin, C. Total iron binding capacity, D. Transferrin saturation
B: Serum ferritin
Answer: B: Serum ferritin 
Explanation: ANSWER: (B) Serum ferritinREF: Harrison's 18th ed ch: 103"Serum ferritin is the most specific and sensitive test for iron deficiency"Under steady-state conditions, the serum ferritin level correlates with total body iron stores; thus, the serum ferritinlevel is the most convenient laboratory test to estimate iron stores.