This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Medicine
[{'content': 'The earliest sign of iron deficiency anaemia - \nSelect and explain. \nA. Increase in iron binding capacity, B. Decrease in serum ferritin level, C. Deorease in serum iron level, D. All the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: <p>Plasma ferritin is a measure of iron stores in tissues & is the single test to confirm iron deficiency .It is a very specific test. In the course of development of anaemia, firstly storage iron(ferritin) depletion occurs during which iron reserves are lost without compromise of the iron supply for erythropoiesis.</p><p>Plasma iron & total iron binding capacity(TIBC) are measures of iron availability ;hence they are affected by many factors besides iron stores.Plasma iron has a diurnal & day -to-day variation & becomes very low in acute phase response .</p>', 'role': 'assistant'}]