Plasma calcium oxalate supersaturation in children with primary hyperoxaluria and end-stage renal failure

Background. Children with primary hyperoxaluria type (PH 1) are at great risk to develop systemic oxalosis in endstage renal disease (ESRD), as endogenous oxalate production exceeds oxalate removal by dialytic therapy. As oxalate accumulates, calcium oxalate (CaOx) tissue deposition occurs. Children with other causes of ESRD, however, are not prone to CaOx deposition despite elevated plasma oxalate (P-Ox) levels. Methods. Our study objective was to examine the potential mechanisms for these observations. We measured P-Ox, sulfate, citrate, and calculated CaOx saturation (beta(CaOx)) in 7 children with ESRD caused by PH 1 and in 33 children with non-PH-related ESRD. Maintenance hemodialysis (HD) was performed in 6 PH 1 and 22 non-PH patients: Pre- and post-HD levels were analyzed at this point and were repeated twice within 12 months in 5 PH 1 and 14 non-PH patients. Samples were obtained only once in 12 patients (one PH 1) on peritoneal dialysis (PD). After liver-kidney or kidney transplantation, plasma levels were measured repetitively. Results. The mean P-Ox was higher in PH (125.7 +/- 17.9 mu mol/liter) than in non-PH patients (44.2 +/- 3.3 mu mol/liter, P < 10(-4)). All other determined anions did not differ between the two groups. beta(CaOx) was higher in PH 1 (4.71 +/- 0.69 relative units) compared with non-PH children (1.56 +/- 0.12 units, P < 10(-4)). P-Ox and beta(CaOx) were correlated in both the PH 1 (r = 0.98: P < 2 x 10(-4)) and the non-PH group (r = 0.98, P < 10(-4)). P-Ox and beta(CaOx) remained stable over time in the non-PH children, whereas an insignificant decline was observed in PH 1 patients after six months of more aggressive dialysis. beta(CaOx) was supersaturated (more than 1) in all PH 1 and in 25 out of 33 non-PH patients. Post-HD beta(CaOx) remained more than 1 in all PH 1, but in only 2 out of 22 non-PH patients. In non PH children. P-Ox and beta(CaOx) decreased to normal within three weeks after successful kidney transplantation. whereas the levels still remained elevated seven months after combined liver-kidney transplantation in two PH patients. Conclusion. Systemic oxalosis in PH 1 children with ESRD is due to higher P-Ox and beta(CaOx) levels. As beta(CaOx) remained supersaturated in PH 1 even after aggressive HD, oxalate accumulation increases, and CaOx tissue deposition occurs. Therefore, sufficient reduction of P-Ox and beta(CaOx) is crucial in PH 1 and might only be achieved by early, preemptive, combined liver-kidney transplantation or liver transplantation alone.