A stimulation test with calcitonin for differential diagnosis of hypercalcaemia

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Abstract
Experimental studies have suggested that in primary hyperparathyroidism (HPT) the cells of the hyperfunctioning parathyroid tissue retain some capacity for stimulation and that an increase in secretion of parathyroid hormone (PTH) can occur when the extracellular Ca concentration is lowered within the hypercalcemic range. This hypothesis was tested in 23 patients with HPT, 10 patients with hypercalcemia of other origin (7 of whom had disseminated malignant disease) and 17 normal subjects. In all 3 groups a single injection of 100 MRC [medical research council] units of salmon calcitonin caused a reduction in serum Ca of approximately 3-5%. In the hypercalemic patients this reduction was correlated to the basal Ca level (r = -0.57, P < 0.01). In the patients with HPT, although they all remained hypercalcemic, the decrease in serum Ca was associated with a mean increase in serum PTH of 10%. Only in 2 patients did such an increase fail to occur despite an adequate decrease in serum Ca. These 2 patients had high basal PTH levels and the lack of response might have been due to a high degree of autonomous parathyroid function. Calcitonin also reduced serum Ca and increased serum PTH in normal subjects. None of the patients with hypercalcemia of other origin than primary HPT displayed a secretory PTH response to serum Ca reduction. This test could be of practical clinical value, particularly in patients with borderline PTH values. A calcitonin-induced rise in PTH while serum Ca is lowered within the hypercalcemic range strongly suggests primary HPT.