Classically, the prototypical form of HC secondary to increased bone resorption is that associated with a primary increase in PTH secretion (namely, primary hyperparathyroidism, PHP), where the increased urinary calcium excretion is due to an increase in filtered calcium due to increased serum calcium concentration that is caused both by the increase in bone resorption, stimulated directly by PTH, and by the increase in intestinal calcium absorption secondary to the increase in calcitriol levels induced by PTH. Here, PTH is linked to primary hyperparathyroidism.