PTH and hyperparathyroidism: On the other hand, sustained elevations of PTH levels by hyperparathyroidism or continuous PTH administration results in loss of bone mass due to excessive bone resorption through the production of receptor activator for nuclear factor-κB ligand (Rankl) in PTH-targeted cells (Bilezikian et al., 2018; Delgado-Calle et al., 2018).