Oxalate removal by hemodialysis in end-stage renal disease

Because of mounting evidence of precipitation of calcium oxalate in the soft tissues of patients with end-stage renal disease (ESRD) on maintenance hemodialysis, the plasma oxalate concentrations and calculated dialysis removal of oxalate were studied in seven patients without evidence of either primary or absorption hyperoxaluria prior to ESRD. A reversed-phase high-pressure liquid chromatographic method was developed to quantitate serum oxalate. Mean value +/- SE in four healthy controls was 28 +/- 5 mumol/L, and in the seven patients it was 187 +/- 15 mumol/L predialysis and 89 +/- 11 mumol/L postdialysis. Oxalate deposition in the soft tissues of ESRD patients is the consequence of sustained hyperoxalemia. Oxalate removal by dialysis was calculated from the four-hour oxalate clearance. Since the ionic radii of phosphate and oxalate are similar, total oxalate clearance was calculated midpoint of dialysis. Mean oxalate removal/dialysis was 3.01 +/- 0.283 mmol. On a daily basis this value was 1.645 +/- 0.155 mmol, which is about threefold the normal oxalate excretion rate. It is not significantly different from the excretion rate in absorption oxalurias but is less than that in primary hyperoxaluria. Therefore, it is concluded that hyperoxalemia in ESRD results from loss of renal excretion, failure of hemodialysis to remove enough oxalate to maintain a normal serum concentration, and increased intestinal absorption of oxalate and/or increased endogenous production.