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
A patient presents with low serum calcium, high phosphorus and elevated 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: Answer is A (Vitamin D levels): Vitamin D deficiency is associated with hypophosphatemia and not hyperphosphatemia Renal failure (t serum creatinine), Pseudohypoparathyroidism (J-CAMP response to PTH) and increased urinary myoglobin (crush syndrome; tissue injury) may all be associated with combination of hypocalcemia, hyperphosphatemia and elevated PTH levels