[Determination of plasma parathyroid hormone in the differential diagnosis of hypercalcemias associated with malignant tumors].

In 44 patients, all suffering from a malignant disease with hypercalcaemia, plasma parathormone was measured by a radioimmunoassay measuring the intact PTH molecule. The results as a function of plasma calcium were compared with those in 38 patients suffering from proven primary hyperparathyroidism and with those in 9 cases of hypercalcaemia of other origin. PTH was indetectable in 14 cases of malignant disease and normal in 25 cases. In 5 patients only could PTH and plasma calcium not be separated from primary hyperparathyroidism. 3 patients had an increased PTH level when plasma calcium was lowered by treatment of the underlying disease. In patients with malignant disease hypercalcaemia is rarely caused by increased secretion of PTH. In these cases either primary hyperparathyroidism or ectopic secretion of PTH may be the cause of hypercalcaemia.