[Incidence of the different types of hypercalciuria in Spain]

To carry out a comparative biochemical study of primary hyperparathyroidism, the different types of hypercalciuria and a healthy population.

Fourteen patients with primary hyperparathyroidism and 103 patients with idiopathic hypercalciuria were studied under conditions of restricted calcium intake and following a calcium load; the results were compared to those of 18 healthy controls.

The patients with hyperparathyroidism showed high parathormone concentrations. Sixty-nine patients with idiopathic hypercalciuria had normal parathormone levels and were considered suffering from absorptive hypercalciuria. Those patients with high urinary calcium excretion under restricted calcium intake and normal urinary phosphate threshold were considered as being absorptive hypercalciuria type I, those with normal urinary calcium as absorptive hypercalciuria type II, and those with low urinary phosphate threshold constituted a renal phosphate leakage group. Thirty-four patients had normal serum calcium, elevated parathormone, hypophosphatemia and high calcium excretion under all dietary conditions, and were considered undergoing renal hypercalciuria. Patients with renal hypercalciuria had increased urine hydroxyproline and low serum calcium compared with the controls after an oral calcium load. This biochemical behaviour is compatible with secondary hyperparathyroidism caused by renal calcium leakage.

In summary, the biochemical parameters: parathormone, urinary phosphate threshold and urinary calcium excretion, measured in fasting conditions, allowed classification of patients with idiopathic hypercalciuria.