Limited calcitonin reserve in hyperparathyroidism.

A comparative study was made of the serum calcitonin levels of patients with hyperparathyroidism. The mean serum calcitonin of those with hyperparathyroidism did not differ significantly from normal persons (mean +/- SEM: 130 +/- 16 pg/ml vs 124 +/- 7 pg/ml, respectively.) Only 0.5% of patients with hyperparathyroidism had values exceeding the upper limits of normal. In contrast, the mean serum calcitonin of patients with hypercalcemia of nonparathyroid etiology was considerably higher than normal (354 +/- 75 pg/ml, p < 0.001)), and 41% exceeded the upper limits of normal. Calcium infusion induced less of an increase in serum calcitonin for patients with hyperparathyroidism than for normal persons. In addition, the diminished responsibility was also present postoperatively. These findings suggest that the prolonged hypercalcemia associated with hyperparathyroidism results in a decreased calcitonin reserve which may persist for unknown reasons. In the clinical evaluation of hypercalcemic patient, the finding of hypercalcitonemia is suggestive evidence against the diagnosis of hyperparathyroidism.