This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nutrition and health, Subject name: Social & Preventive Medicine
[{'content': 'First indices to change in iron deficiency anemia is - \nSelect and explain. \nA. S. Iron, B. Total iron binding capacity, C. S. Ferritin, D. S. Haemoglobin concentration', 'role': 'user'}, {'content': "Answer: C \nExplanation: The single most sensitive tool for evaluating the iron status is by measurement of serum ferritin. Hemoglobin concentration is relatively insensitive. REF. PARK'S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICAL 21ST EDITION. PAGE NO - 623", 'role': 'assistant'}]