How do the serum calcium level and dietary sodium intake affect hypercalciuria?
To help prevent hypercalcemia, nonrenal elevation in serum calcium causes an increase in both filtered calcium and urinary calcium. Increased sodium delivery to Henle’s loop and the distal tubule also raises urinary calcium. In non–stone formers, urinary calcium excretion increases about 40 mg for each 100 mEq of sodium excretion. In patients with hypercalciuric stones, calcium excretion increases up to 80 mg per each 100 mEq of sodium. Because urinary sodium excretion increases with higher dietary sodium intake, restricting dietary sodium reduces urinary calcium excretion. In patients with renal stones, the recommended daily dietary sodium is < 100 mEq (2300 mg) or about one teaspoon of salt (6000 mg).