Variability in urinary oxalate measurements between six international laboratories

Naim M. Maalouf, Beverley Adams Huet, Andreas Pasch, John C. Lieske, John R. Asplin, Roswitha Siener, Albrecht Hesse, Jean Marc Nuoffer, Felix J. Frey, John Knight, Ross P. Holmes, Joseph E. Zerwekh, Olivier Bonny

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Background. Hyperoxaluria is a major risk factor for kidney stone formation. Although urinary oxalate measurement is part of all basic stone risk assessment, there is no standardized method for this measurement. Methods. Urine samples from 24-h urine collection covering a broad range of oxalate concentrations were aliquoted and sent, in duplicates, to six blinded international laboratories for oxalate, sodium and creatinine measurement. In a second set of experiments, ten pairs of native urine and urine spiked with 10 mg/L of oxalate were sent for oxalate measurement. Three laboratories used a commercially available oxalate oxidase kit, two laboratories used a high-performance liquid chromatography (HPLC)-based method and one laboratory used both methods. Results. Intra-laboratory reliability for oxalate measurement expressed as intraclass correlation coefficient (ICC) varied between 0.808 [95% confidence interval (CI): 0.427-0.948] and 0.998 (95% CI: 0.994-1.000), with lower values for HPLC-based methods. Acidification of urine samples prior to analysis led to significantly higher oxalate concentrations. ICC for inter-laboratory reliability varied between 0.745 (95% CI: 0.468-0.890) and 0.986 (95% CI: 0.967-0.995). Recovery of the 10 mg/L oxalate-spiked samples varied between 8.7 ± 2.3 and 10.7 ± 0.5 mg/L. Overall, HPLC-based methods showed more variability compared to the oxalate oxidase kit-based methods. Conclusions. Significant variability was noted in the quantification of urinary oxalate concentration by different laboratories, which may partially explain the differences of hyperoxaluria prevalence reported in the literature. Our data stress the need for a standardization of the method of oxalate measurement.

Original languageEnglish (US)
Pages (from-to)3954-3959
Number of pages6
JournalNephrology Dialysis Transplantation
Issue number12
StatePublished - Dec 2011


  • agreement
  • hyperoxaluria
  • method
  • oxalate
  • stone

ASJC Scopus subject areas

  • Nephrology
  • Transplantation


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