Clinical Studies on Phosphate Handling in Hypercalcaemia

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Abstract
Phosphate indices (serum phosphate, tubular reabsorption of phosphate, renal threshold phosphate concentration (TmP/GFR) and index of phosphate excretion) were studied in 88 hypercalcemic subjects: 64 with primary hyperparathyroidism (HPT) and 24 with hypercalcemia from other causes, predominantly malignant disease. HPT patients as a group could easily be separated from normal subjects (n = 16) and patients with functional hypoparathyroidism (n = 7) by use of the phosphate variables, but these indices were of little discriminating value for the differential diagnosis between HPT and hypercalcemia from other causes. There was no difference in the urinary cAMP excretion between the 2 hypercalcemic patient groups, but HPT patients had clearly elevated serum parathyroid hormone (PTH) levels compared with normal PTH concentrations in patients with other causes of hypercalcemia. A positive correlation between cAMP and serum Ca and an inverse relationship between cAMP and serum Ca and an inverse relationshiop between cAMP and TmP/GFR were found in patients with hypercalcemic malignant disease. A humoral factor with PTH-like effects may exist in malignant disease. Since PTH levels were low, the physiological actions were apparently not mediated by circulating PTH. No difference in the values for phosphate variables, PTH, cAMP or serum Ca was found between renal stone-forming and stone-free patients with HPT.