Kidney Week

Abstract: PO0417

Assessment of Blood Oxalate Concentrations in Patients with CKD

Session Information

• Calcified Tissues in Kidney Diseases
  October 22, 2020 | Location: On-Demand
  Abstract Time: 10:00 AM - 12:00 PM

Category: Bone and Mineral Metabolism

• 402 Bone and Mineral Metabolism: Clinical

Authors

• Pfau, Anja Christine, Charite Universitatsmedizin Berlin, Berlin, Berlin, Germany

Anja Christine Pfau,

• Wytopil, Monika, Universitatsklinikum Erlangen, Erlangen, Bayern, Germany

Monika Wytopil,

• Chauhan, Kinsuk, Icahn School of Medicine at Mount Sinai, New York, New York, United States

Kinsuk Chauhan,

• Reichel, Martin, Charite Universitatsmedizin Berlin, Berlin, Berlin, Germany

Martin Reichel,

• Coca, Steven G., Icahn School of Medicine at Mount Sinai, New York, New York, United States

Steven G. Coca,

• Aronson, Peter S., Yale University Department of Internal Medicine, New Haven, Connecticut, United States

Peter S. Aronson,

• Eckardt, Kai-Uwe, Charite Universitatsmedizin Berlin, Berlin, Berlin, Germany

Kai-Uwe Eckardt,

• Knauf, Felix, Charite Universitatsmedizin Berlin, Berlin, Berlin, Germany

Felix Knauf,

Background

Alterations in oxalate homeostasis are associated with kidney stone disease and progression of chronic kidney disease (CKD). However, accurate measurement of plasma oxalate (P_Ox) 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 P_Ox results. Subsequently, a standardized analytical protocol was established, and P_Ox concentrations were measured in a large cohort of patients with CKD.

Methods

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

Results

P_Ox concentrations increased rapidly when samples were maintained at RT. This was most relevant for P_Ox < 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 P_Ox measurement was 44.0 (17.9) ml/min/1.73 m². More than half of the patients had a P_Ox concentration below 2.0 µM. P_Ox 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 P_Ox of 2.7 µM (IQR 1.9 – 4.2).

Conclusion

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

Funding

• Commercial Support – Dicerna Pharmaceuticals, Cambridge, USA