Calcium oxalate saturation in dialysis patients with and without primary hyperoxaluria

Calcium oxalate supersaturation of the blood is associated with deposition of crystals in various tissues. We measured the serum levels of oxalate, citrate, calcium, and magnesium to estimate their saturation in 112 hemodialysis patients without primary hyperoxaluria and two boys with primary hyperoxaluria. Serum levels of oxalate and citrate were determined by high-performance capillary electrophoresis, while calcium and magnesium were measured by ICP spectroscopy. The serum levels of oxalate, citrate, calcium, and magnesium were 44.9 +/- 16.5, 138.1 +/- 54.9 mu mol/l, 2.30 +/- 0.28, and 1.07 +/- 0.18 mmol/l, respectively, while the levels in patients with primary hyperoxaluria were 83.9 +/- 34.3, 197.9 +/- 63.5 mu mol/l, 2.53 +/- 0.15, and 1.14 +/- 0.34 mmol/l, respectively. Serum calcium oxalate saturation (SS), as calculated by the Equil program, was significantly correlated with the serum oxalate level. Most patients showed metastable supersaturation (1 < SS < 8.9), which was associated with a serum oxalate level of more than 30 mu mol/l. Serum saturation exceeded the formation product (SS=8.9) in some specimens from patients with type 1 primary hyperoxaluria. The serum calcium oxalate saturation [SS(CaOx)] showed a significant positive correlation with the levels of oxalate [Ox], calcium [Ca], and citrate [Cit]: [SS(CaOx)] = - 0.3562 + 34.634[OX] + 0.394[Ca]- 0.483[Mg] + .101[Cit], (all mmol/l, r=0.9848, P < 0.01). This formula is useful for estimating the saturation. In conclusion, the serum oxalate level is a good indicator of calcium oxalate saturation and should be monitored accurately while keeping it lower in dialysis patients.