A unified liquid chromatography–mass spectrometry (LC-MS) method for quantitation of biomarkers of inherited metabolic disorders associated with urolithiasis

Abstract Background and Aims Inborn metabolic diseases (IMD) are important causes of urolithiasis in paediatric and adult patients. Especially when stones arise at a young age the screening for IMD related biomarkers is warranted. The diagnostic reports often over-report by not only giving results on the specific metabolites important for stone formation, but also on all other metabolites quantified in those assays. We aimed at developing and implementing a simplified quantitative method to consolidate three assays in one targeted LC-MS urolithiasis screening. In this screening method we included nine key metabolites involved in purine, pyrimidine, glyoxylate, and amino acid metabolism. This method consolidates three classical assays (amino acids quantification, purine & pyrimidine quantification and organic acids analysis) into one simplified workflow. Methods analysis of nine metabolites, and their individual internal standards, in urine was achieved with a run-to-run time of 35 minutes by LC- MS. Results We successfully validated this new method with a good correlation with the previously used three separate assays. Urine pH did hardly affect metabolite quantification. Age-dependent reference ranges were established and patient samples from persons with a confirmed IMD were all correctly identified in the clinical validation. Conclusions This streamlined assay supports improved implementation of urinary metabolic screening in urolithiasis workups.