Background: Measurement of plasma oxalate (POx) is challenging, but critical, for management of patients with primary hyperoxaluria type 1. A novel LC–MS/MS assay was developed, validated and used to quantify POx in patients with primary hyperoxaluria type 1. Methods: Samples (100 μl of plasma in K2EDTA) were spiked with internal standard (13C2-labeled oxalic acid), acidified and cleaned by protein precipitation before analysis using anion HPLC–ESI–MS/MS. The assay was validated with a quantitation range of 0.500–50.0 μg/ml (5.55–555 μmol/l). All parameters successfully met acceptance criteria, including 15% (20% at lower limit of quantification) for accuracy and precision. Conclusion: This assay has advantages over previously published POx quantitation methods, was validated in accordance with regulatory guidelines and accurately determined POx levels in humans.
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