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Abstract: SA-PO1026

Evaluation of Plasma Oxalate Measurements

Session Information

Category: Pathology and Lab Medicine

  • 1800 Pathology and Lab Medicine


  • Cardozo, Lila, NYU Langone Health, New York, New York, United States
  • Pierce, Kerry A., Broad Institute, Cambridge, Massachusetts, United States
  • Zaidan, Nadim, NYU Langone Health, New York, New York, United States
  • Xiong, Xiaozhong, NYU Langone Health, New York, New York, United States
  • Clish, Clary B., Broad Institute, Cambridge, Massachusetts, United States
  • Nazzal, Lama, NYU Langone Health, New York, New York, United States

Oxalate is a uremic retention solute that accumulates in end-stage kidney disease since it is not efficiently removed by hemodialysis (HD). This increased plasma oxalate (POx) has been associated with higher cardiovascular (CV) mortality in HD patients. Oxalate is usually measured by oxalate oxidase methods, however, multiple large trials are now measuring metabolites using global metabolomics platforms allowing a great opportunity to mine data and identify associations between POx and CV outcomes. Our goal was to evaluate the congruence between targeted and untargeted methods.


We assessed oxalate in plasma samples previously collected during the pretreatment phase for a study evaluating inulin in HD patients (PMID: 35369018). In this post-hoc analysis, we measured POx in plasma samples for 12 HD patients, both at baseline and after 8 weeks. We first used the Trinity Oxalate Kit, with a protocol adapted for plasma samples. We then sent the same samples to the Broad Institute for HPLC coupled with Mass Spectrometry (MS). This metabolomics assessment was done in duplicate, and on thawed and non-thawed samples. Oxalate measurements were then calculated from a calibration curve using isotopically-labeled oxalic acid.


First, based on the colorimetric output, POx ranged from 115 µM to 23 µM with a mean of 57.38 µM ± 27.94 µM. Based on the MS output, POx ranged from 17 to 31µM with a mean of 22.98 µM ± 3.17 µM, which is within the range described in the literature. POx levels were stable over 2 months for each patient. This low within-subjects variability highlights the stability of POx levels in the HD population. Regarding temperature effect, thawed sample values were 4% higher on average than non-thawed samples. Finally, a comparison of the colorimetric and the MS methods showed consistently higher colorimetric POx levels, on average 2.43-fold higher.


By quantifying oxalate in HD patients using a commercial metabolomics platform and an enzymatic bench assay, we identified a discrepancy between both measurements. Leaving the samples at room temperature did not majorly affect the MS output. Next steps will involve the optimization of the bench colorimetric assay.


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