Increasing parathyroid hormone concentrations in untreated primary hyperparathyroidism.

Twenty-four patients with mild to moderate primary hyperparathyroidism were followed for an average of 2.45 years with serial determinations of serum ionized calcium and intact parathyroid hormone (PTH). For the entire group serum ionized calcium remained stable, whereas serum PTH increased significantly. Eleven patients (group 1) demonstrated a significant increase in PTH with time. The remaining 13 patients formed group 2. Comparison of the changes (%) in each subgroup showed a small but significant increase in serum ionized calcium of 2.6% with time in group 1, while serum PTH increased by 78%. In group 2 serum ionized calcium remained stable whereas PTH increased modestly by 22%. Serum concentrations of creatinine were stable throughout the follow-up period in both groups. Despite the greater precision of serum ionized calcium, measurements of intact PTH are evidently more sensitive than measurements of serum ionized calcium for the detection of progression in primary hyperparathyroidism.