Contribution of dialysis to endogenous oxalate production in patients with chronic renal failure.

We tested the possibility that the buffering agents in dialysis bath fluid might contribute to increased endogenous oxalate production in dialyzed patients. Using stable isotope dilution mass spectrometry, we obtained oxalate production rates and pool sizes directly for 10 patients in chronic renal failure, 5 of whom were undergoing continuous ambulatory peritoneal dialysis (lactate-buffered fluid). All peritoneal dialysis patients had either increased oxalate production rates or expanded oxalate pools when compared with undialyzed patients in renal failure. From a further four patients receiving maintenance hemodialysis we took blood samples immediately before and after three consecutive dialysis sessions in which the bath-fluid buffering agent (bicarbonate or acetate) was alternated; we analyzed these samples for oxalate and key precursors by capillary gas chromatography. Plasma glycine and serine concentrations remained within the physiological range. Glycolate and oxalate concentrations decreased, but the oxalate remained above normal after dialysis. All changes were independent of the bath-fluid buffering agent. We suggest that dialysis might stimulate the formation of oxalate by removing product inhibition of a late catabolic step.