Renal oxalate excretion in calcium urolithiasis

Urinary oxalate was determined in an ambulatory setting in 107 patients with an increased intestinal calcium absorption rate in whom stones formed, 34 patients with normal calcium absorption in whom stones formed and 34 control subjects without stones. Urinary oxalate excretion was not significantly different when the diet was changed from a random to a calcium-restricted diet. Moreover, urinary oxalate was not higher during summer months when intestinal calcium absorption may have been stimulated. Diet history disclosed that many patients with an increased calcium absorption rate had been on a moderate oxalate-restricted diet, often as part of a calcium-restricted regimen for the control of hypercalciuria. The results indicate that renal oxalate excretion in an ambulatory setting is not critically dependent on the state of calcium absorption and intake, and that the imposition of a low calcium dietary regimen in patients with an increased calcium absorption and in whom stones form does not necessarily augment oxalate excretion.