[Incidence of hyperoxaluria in idiopathic calcium nephrolithiasis]

Urinary excretion rate of oxalate was measured in 79 patients with idiopathic calcium (Ca) nephrolithiasis and the results were compared with those obtained in 28 healthy volunteers. The group of stone formers consisted of 20 patients with idiopathic hypercalciuria (IHC) of the absorptive type, 23 patients with IHC of the renal type, 11 patients with hypercalciuria secondary to dietary factors, 1 patient with hyperuricosuria (as an isolated finding) and 24 patients without hypercalciuria nor hyperuricosuria. Classification was based upon the urinary excretion rate of uric acid, as well as that of calcium measured under 3 different dietary conditions (i.e. free diet, free diet supplemented with 3 g Ca/day for 3 days, and diet free of dairy products for 5 days). On a free diet, normal values of oxaluria ranged from 125 to 435 mumol/24 h; an elevated value was observed in 11 (14%) patients, 5 of whom belonged to the subgroup without hypercalciuria nor hyperuricosuria. On a low Ca diet, mild hyperoxaluria occurred in 3 controls and in 19 patients, the tendency to develop hyperoxaluria being particularly marked in the subgroup with absorptive-IHC. Moreover, there was a positive correlation between oxaluria on a low Ca diet and the estimated degree of intestinal absorption of Ca. This study confirms the finding that on a free diet, the incidence of mild hyperoxaluria amongst idiopathic stone formers is rather low. It shows, however, that a significant percentage of patients classically referred to as "without metabolic disorder" have in fact slight hyperoxaluria, an observation with a potential therapeutic impact. Finally, it shows that on a low Ca diet, patients with absorptive-IHC are particularly prone to develop hyperoxaluria: the latter observation renders questionable the relevance of a low Ca diet for patients with absorptive IHC, unless their intake of oxalate is simultaneously reduced.