A theoretical analysis of the steady-state relationship between plasma concentrations of calcium and parathyroid hormone.

A theoretical consideration of the relationship between plasma concentrations of calcium and parathyroid hormone suggests that the reported negative correlations between these variables in normal subjects and in patients with secondary hyperparathyroidism, and the positive correlation in patients with primary hyperparathyroidism, may be fortuitous and do not necessarily imply fundamental differences in the negative feedback mechanism.