This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
A patient presents with low serum calcium, high phosphorus and etevated PTH. Which of the following investigations is least contributory to establish a diagnosis - 
Select and explain. 
A. Vitamin D levels, B. Serum creatinine levels, C. Cyclic AMP response to PTH, D. Urine myoglobin
A: Vitamin D levels
Answer: A: Vitamin D levels 
Explanation: Ans is option 1.. Vit D levels Vit d deficiency is associated with hypophosphatemia and not hyperphosphatemia Renal failure, pseudohypoparathyroidism and increased urinary myoglobin may all be associated with combination of hypocalcemia, hyperphosphatemia and elevated PTH levels Ref Harrison 19/e p2482