<prompt> A patient presents with low serum calcium, high phosphorus and etevated PTH. Which of the following investigations is least contributory to establish a diagnosis -Vitamin D levelsSerum creatinine levelsCyclic AMP response to PTHUrine myoglobin  <response>: 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 19e p2482 