PTH and secondary hyperparathyroidism: For primary hyperparathyroidism, the range of PTH level varies from normal in some patients to >65 pg/mL in most patients, whereas for secondary hyperparathyroidism, the range of PTH levels is dependent on the primary process that causes hypercalcemia, but is above 65 pg/mL.[11,12] The highest values of PTH are associated with end-stage renal disease (ESRD), with levels from 2 to 9 times above the upper physiological range.[13] An understanding of the genetic regulation of serum PTH levels could be of valuable clinical importance.