Clinical significance of the heterogeneity of parathyroid hormone.

Circulating immunoreactive PTH consists primarily of intact hormone and a biologically inactive C-terminal fragment. About half of the intact PTH is removed by the kidney and half by other mechanisms. In contrast, the kidney appears almost solely responsible for removal of the C-terminal fragment. There have as yet not been definitive answers to the following questions: Where in the body is the long-lived C-terminal fragment produced? What is the quantitative relation between the disappearance half-time of the C-terminal fragment and some measure of the stage of kidney dysfunction? What is the true prevalence of ectopic PTH production?