Plasma oxalate following kidney transplantation in patients without primary hyperoxaluria.

BACKGROUND: Patients with primary hyperoxaluria may need repeated kidney transplants due to damage from oxalic acid (oxalate) deposits. However, oxalate may also be potentially harmful in all transplant recipients. Determinants of oxalate following transplantation have not been well studied. METHODS: Two hundred and twelve recipients admitted for transplantation were included in the study. Blood samples for measurement of oxalate and other relevant laboratory parameters were collected at baseline and subsequently 10 weeks after transplantation. For oxalate determination, samples were obtained in 99, 167 and 54 patients out of the 212 at baseline, at follow-up and at both time points, respectively. We examined the bivariate association between plasma oxalate at transplantation and preemptive transplantation, time on dialysis, recipient age, creatinine, urea, phosphate, haemoglobin, PTH, albumin and calcium. Oxalate 10 weeks after transplantation was tested likewise including also laboratory parameters at baseline, primary non-function, rejection episodes, live versus deceased donor, donor age and GFR at follow-up. RESULTS: Median plasma oxalate concentration at transplantation was 35.0 micromol/L [95% confidence interval (95% CI) = 10.4-93.9] and 98% of the values were above normal limits (2.6-11.0). Oxalate concentration after 10 weeks was 9.0 micromol/L (4.0-25.5), still 37% being above the upper normal value. Multiple regression analysis revealed established dialysis treatment (P = 0.002) and creatinine (P < 0.000001) as independent positive determinants of oxalate at transplantation. Oxalate at 10 weeks was negatively associated to (51)Cr-EDTA absolute GFR (P = 0.023) and positively associated to donor age (P = 0.027) and plasma creatinine at 10 weeks (P = 0.03). CONCLUSION: At transplantation, plasma oxalate was on average three times increased and above the upper normal limit in 98% of patients and were still above normal in 37% after 10 weeks. The reduction after 10 weeks is determined by GFR and donor age. Whether increased plasma oxalate following kidney transplantation may have long-term consequences needs further study.