Effect of Calcium Restriction on Renal Excretion of Oxalate and the Probability of Stones in the Various Pathophysiological Groups with Calcium Stones

Abstract

To evaluate the adequacy of simple Ca restriction for patients with idiopathic Ca stones, the effect of 5 days of Ca restriction without oxalate restriction on renal excretion of Ca and oxalate, and the corresponding probability of stones, were assessed in 50 controls and 48 patients. Renal excretion of Ca decreased and that of oxalate increased significantly in all groups, but the importance of the changes was critically dependent upon the underlying pathophysiological condition. The probability of stones decreased only in patients with absorptive hypercalciuria type II owing to the usual excessive calcium intake and increased in those with absorptive hypercalciuria type I and renal hypercalciuria, which are associated with true hyperabsorption of Ca and represent the 2 forms of idiopathic hypercalciuria. Simple Ca restriction may be beneficial for patients with idiopathic calculi only when the hypercalciuria is caused by exaggerated intake of Ca, since it increases the probability of stones in patients with idiopathic hypercalciuria. Ca restriction always is associated with an increase in oxalate excretion, suggesting that simultaneous oxalate restriction should be added in all cases to decrease the probability of stones.