Quantification of Oxalate by Novel LC–MS/MS: Assay Development, Validation and Application in Lumasiran Clinical Trials

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.A novel assay to measure plasma oxalate was developed and validated successfully in accordance with regulatory guidelines. The required sample volume was only 100 μl of plasma, which is especially favorable in the pediatric population, and there is no need to acidify blood at the collection site before processing. The assay accurately determines plasma oxalate levels, which were used as a measure of efficacy in the lumasiran clinical trials.