The Effect of High Parathyroid Hormone Concentration on Calcitonin in Patients with Primary Hyperparathyroidism2)

: Serum calcitonin (CT), parathyroid hormone (PTH), and calcium levels were measured in 23 patients with primary hyperparathyroidism. PTH was determined by a midregion (M-RIA) and a carboxyl-terminal (C-RIA) specific PTH-RIA. Only 2 patients had elevated CT levels. In contrast to the findings in 46 healthy controls, the CT levels did not correlate with calcium levels. Patients who had the highest iPTH values showed a negative correlation between CT and iPTH (M-RIA (n = 7): R = -1.0000, p less than 0.001; C-RIA (n = 13): R = -0.5604, p less than 0.05). The results of the C-RIA were subtracted from those of the M-RIA. In 12 patients with the highest levels of intact PTH (M-RIA - C-RIA), serum PTH concentration was inversely correlated with serum CT concentration (R = -0.7343, p less than 0.01). In the same patients a negative correlation between CT and calcium was found (R = -0.6783, p less than 0.02). These findings suggest that high PTH levels may have a direct suppressive effect on CT concentration and this may be, at least in part, responsible for failure of CT concentrations to rise in many patients with primary hyperparathyroidism.