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Kidney Week

Abstract: PO0417

Assessment of Blood Oxalate Concentrations in Patients with CKD

Session Information

Category: Bone and Mineral Metabolism

  • 402 Bone and Mineral Metabolism: Clinical


  • Pfau, Anja Christine, Charite Universitatsmedizin Berlin, Berlin, Berlin, Germany
  • Wytopil, Monika, Universitatsklinikum Erlangen, Erlangen, Bayern, Germany
  • Chauhan, Kinsuk, Icahn School of Medicine at Mount Sinai, New York, New York, United States
  • Reichel, Martin, Charite Universitatsmedizin Berlin, Berlin, Berlin, Germany
  • Coca, Steven G., Icahn School of Medicine at Mount Sinai, New York, New York, United States
  • Aronson, Peter S., Yale University Department of Internal Medicine, New Haven, Connecticut, United States
  • Eckardt, Kai-Uwe, Charite Universitatsmedizin Berlin, Berlin, Berlin, Germany
  • Knauf, Felix, Charite Universitatsmedizin Berlin, Berlin, Berlin, Germany

Alterations in oxalate homeostasis are associated with kidney stone disease and progression of chronic kidney disease (CKD). However, accurate measurement of plasma oxalate (POx) concentration is challenging as prompt processing and acidification of samples has been deemed necessary. In the present study we examined the effects of variations in sample handling on POx results. Subsequently, a standardized analytical protocol was established, and POx concentrations were measured in a large cohort of patients with CKD.


We tested the effects on POx results of storage time at room temperature (RT), storage on dry ice and maintenance of samples at -80°C. POx was measured in 1826 patients enrolled in the German Chronic Kidney Disease (GCKD) study, an ongoing multicenter, prospective, observational cohort study.


POx concentrations increased rapidly when samples were maintained at RT. This was most relevant for POx < 10 µM as concentrations more than doubled within a few hours. Immediate freezing on dry ice and storage at -80°C provided stable results and allowed postponement of acidification for > 1 year. In the GCKD study, mean (SD) eGFR at the time of POx measurement was 44.0 (17.9) ml/min/1.73 m2. More than half of the patients had a POx concentration below 2.0 µM. POx correlated positively with urinary albumin to creatinine ratio and inversely with eGFR (P <0.001). In the lowest eGFR quartile, median eGFR was 25.1 ml/min/1.73 m2 (IQR 20.3 - 28.1) with a median POx of 2.7 µM (IQR 1.9 – 4.2).


We conclude that immediate freezing and maintenance of plasma samples at -80°C facilitates the sample collection process and allows accurate POx assessment in large patient cohorts. Our study presents a critical and useful modification of the complex preanalytical procedure. Moreover, we demonstrate that POx concentrations in patients with CKD are substantially lower than previously reported. The present study may serve as a reference for sample handling to assess POx in clinical trials and to determine its role in CKD progression.


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