Abstract
Abstract Background and Aims High oxalic acid concentration may be caused by genetic disorders, enteric diseases, but also by kidney insufficiency per se. It may result in kidney oxalic acid stones, kidney function decline, and failure. This study aimed to investigate whether dietary oxalic acid intake influences plasma oxalic acid concentration in a population undergoing kidney transplantation. Method Dietary oxalic acid intake was assessed using a Food Frequency Questionnaire. Based on frequency and portion size, average daily oxalic acid intake in the past year and in the last 24 hours was calculated. A blood sample for determination of plasma oxalic acid concentration was drawn on the operation ward before transplantation. For multivariable analysis seventeen recipient related variables were gathered. Results 418 patients were included. The median age of the participants was 62 year, 60% were male, all had an eGFR <20 ml/min/1.73 m2, and 66% were on dialysis with a median dialysis vintage of 13 months. The median plasma oxalic acid concentration was 32.2 µmol/L (range 4.6-243.2). In 98.3% of patients oxalic acid concentration was above the upper limit of normal. The average oxalic acid intake was 199 mg/day (range 4-1599), while it was 138 mg/day in the last 24 hours before transplantation (range 0-3906). Multivariable linear regression analysis showed that plasma oxalic acid concentrations were significantly higher in recipients with higher average (p<0.001) and last 24 hours oxalic acid intake (p = 0.002), lower age (p<0.001), lower residual diuresis (p<0.001), higher body mass index (p<0.001), longer dialysis vintage (p = 0.032), hemodialysis (p<0.001), and peritoneal dialysis (p<0.001) versus preemptive status. Conclusion In pre-kidney transplant patients, plasma oxalic acid concentration is above upper normal limit in 98.3% of patients and is multifactorially determined. As all other factors are not modifiable, the only way to decrease plasma oxalic acid concentration is dietary restriction.
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