This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'A patient presents with low serum calcium, high phosphorus and elevated PTH. Which of the following investigations is least contributory to establish a diagnosis - \nSelect and explain. \nA. Vitamin D levels, B. Serum creatinine levels, C. Cyclic AMP response to PTH, D. Urine myoglobin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]