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: Pathology
Most sensitive indicator for Iron deficiency anaemia? 
Select and explain. 
A. Serum Ferrtin, B. TIBC, C. Percentage saturation of transferrin, D. Bone marrow iron
A: Serum Ferrtin
Answer: A: Serum Ferrtin 
Explanation: Ref: CMDT 2019, P 512* Low ferritin levels <12ng/ml is a highly reliable indicator of reduced iron stores. Serum ferritin can increase in response to inflammation and hence normal or elevated ferritin level does not exclude diagnosis of IDA.* As iron deficiency progresses iron levels will be less than 30mcg/dl and transferrin levels rise to compensate.* The elevated transferrin leads to lower saturation to <15%.