Effects of mineral composition of drinking water on risk for stone formation and bone metabolism in idiopathic calcium nephrolithiasis.

1. To assess whether the mineral content of drinking water influences both risk of stone formation and bone metabolism in idiopathic calcium nephrolithiasis, 21 patients were switched from their usual home diets to a 10 mmol calcium, low-oxalate, protein-controlled diet, supplemented with 21 of three different types of mineral water. Drinking water added 1, 6 and 20 mmol of calcium and 0.5, 10 and 50 mmol of bicarbonate respectively to the controlled diet. 2. The three controlled study periods lasted 1 month each and were separated by a 20 day washout interval. Blood and urine chemistries, including intact parathyroid hormone, calcitriol and two markers of bone resorption, were performed at the end of each study period. The stone-forming risk was assessed by calculating urine saturation with calcium oxalate (beta CaOx), calcium phosphate (beta bsh) and uric acid (beta UA). 3. The addition of any mineral water produced the expected increase in urine output and was associated with similar decreases in beta CaOx and beta UA, whereas beta bsh varied marginally. These equal decreases in beta CaOx, however, resulted from peculiar changes in calcium, oxalate and citrate excretion during each study period. The increase in overall calcium intake due to different drinking water induced modest increases in calcium excretion, whereas oxalate excretion tended to decrease. The changes in oxalate excretion during any one study period compared with another were significantly related to those in calcium intake. Citrate excretion was significantly higher with the high-calcium, alkaline water. 4. Parathyroid hormone, calcitriol and markers of bone resorption increased when patients were changed from the high-calcium, alkaline to the low-calcium drinking water. 5. We suggest that overall calcium intake may be tailored by supplying calcium in drinking water. Adverse effects on bone turnover with low-calcium diets can be prevented by giving high-calcium, alkaline drinking water, and the stone-forming risk can be decreased as effectively as with low-calcium drinking water.

Determinants of oxalate balance in patients on chronic peritoneal dialysis.

We assessed plasma levels and removal rates of oxalate in 24 patients on chronic peritoneal dialysis (CPD) for oxalosis-unrelated renal failure. The ion-chromatographic (IC) measurements of oxalate in plasma, dialysate, and urine (in seven patients with residual renal function) were used to calculate peritoneal and renal clearances of oxalate. The serum state of saturation with calcium oxalate was calculated by means of a computer-based model system. Patient data were compared with those from 19 healthy individuals. Peritoneal clearance of oxalate was 6.3 +/- 4.7 mL/min, ie, 8% of the normal renal clearance. As a result, both plasma oxalate and calcium oxalate saturation were higher than in controls and did not overlap. Plasma was supersaturated with calcium oxalate in only two of 24 patients (8%). Removal of oxalate by dialysis was related to the amount of fluid infused. Overall removal of oxalate (dialysate plus urine) was similar to 24-hour excretion of normal subjects and was taken as a measure of its generation. Oxalate generation rate was dependent on protein (whole and animal) intake, but not on caloric intake or pyridoxine status. Pyridoxine supplementation, 75 and 300 mg daily for 1 months, was not effective in reducing plasma levels or generation rates of oxalate. Residual renal function had a minor influence on oxalate patterns. We conclude that current programs are adequate to maintain oxalate balance in patients on CPD under basic conditions.

Preventing ascorbate interference in ion-chromatographic determinations of urinary oxalate: four methods compared.

In an attempt to decrease ascorbate interference on the ion-chromatographic determination of urinary oxalate, we compared the effectiveness of four different methods for ascorbate elimination by analyzing a representative urine pool supplemented with successive ascorbate additions. Two of the methods--treatment with ferric ions or boric acid--have been described elsewhere; treatments with nitrites or ascorbate oxidase (EC 1.10.3.3) are investigated here as possible alternatives. Consideration of the main features, advantages, and drawbacks of the four procedures leads us to conclude that boric acid dilution is a good routine method and that pre-incubation with ascorbate oxidase reliably prevents ascorbate interference in assays of urinary oxalate.