This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Physiology
[{'content': 'Earliest change in iron deficiency anaemia is \nSelect and explain. \nA. Decreased serum iron, B. Decreased serum ferritin, C. Decreased TIBC, D. Decreased hemoglobin', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ferritin is a blood cell protein that contains iron. A ferritin test helps your doctor understand how much iron your body is storing. If a ferritin test reveals that your blood ferritin level is lower than normal, it indicates your body's iron stores are low and you have iron deficiency Ref:guyton and hall textbook of medical physiology 12 edition page number:118,119,120", 'role': 'assistant'}]