High Plasma Oxalate Levels Early After Kidney Transplantation Are Associated With Impaired Long-Term Outcomes.

Background: Elevated levels of oxalate are common in renal failure patients and non-hyperoxaluria disease, and may cause damage after transplantation. We examined outcomes after 15 years for 167 kidney transplant recipients who had plasma oxalate measured early after transplantation. Analyses included plasma oxalate, recipient age, donor age, live donor, HLA-DR mismatch, mGFR, and smoking. Results: Median age was 52 years (range 18-81), 63% were male and 38% had live donors. Median plasma oxalate concentration 10 weeks after transplantation was 9.0 µmol/L (range 2.7-53.0), one third above the upper reference limit (11.0 µmol/L). Multivariable analysis revealed upper quartile plasma oxalate (>13.0 µmol/L, p = 0.008), recipient age (p < 0.001), deceased donor (p = 0.003), and current smoking (p < 0.001) as significant factors associated with patient survival. Upper quartile plasma oxalate (p = 0.021), recipient age (p = 0.001), deceased donor kidney (p = 0.001), HLA-DR mismatch (p = 0.015), and current smoking (p = 0.014) were also associated with graft loss. Factors associated with death censored graft losses were donor age (p = 0.012), deceased donor (p = 0.032), and HLA-DR mis-matched kidneys (p = 0.005) but plasma oxalate was not (p = 0.188). Conclusions: Plasma oxalate in the upper quartile early after transplantation was significantly associated with impaired long-term patient survival and graft losses, but not when censored for death.

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.