Serum ionized calcium and parathyroid hormone in renal stone disease.

Serum ionized calcium was shown to be significantly elevated in a group of twenty-eight subjects with idiopathic hypercalciuria in whom the mean total serum calcium concentration was within normal limits. Measurement of parathyroid hormone levels confirmed that elevated values are suppressible by infusion of calcium. Ten subjects with simultaneous elevation of serum ionized calcium and parathormone levels above 3 S.D. of normal were referred for neck exploration, and a parathyroid adenoma was found and removed in nine. Significant decreases to normal values of serum ionized calcium and parathormone levels of urine and calcium excretion were documented some weeks following operation. The results conflict with both the alimentary calcium hyperabsorption theory and the renal calcium leak theory of the aetiology of idiopathic hypercalciuria, and support the possibility that idiopathic hypercalciuria in many cases represents an early or mild form of 'normocalcaemic' primary hyperparathyroidism.