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
[{'content': 'Most sensitive indicator for Iron deficiency anaemia? \nSelect and explain. \nA. Serum Ferrtin, B. TIBC, C. Percentage saturation of transferrin, D. Bone marrow iron', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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%.', 'role': 'assistant'}]