PTH and Hypercalcemia: Severe hyperparathyroidism that is refractory to medical therapy and associated with hypercalcemia (in the absence of medications such as calcitriol, vitamin D, or calcium-containing phosphate binders) suggests tertiary hyperparathyroidism, in which there is autonomous secretion of PTH that is not responsive to the plasma calcium concentration [3, 5, 7, 8, 10, 11, 30–35].