Quantitative analysis of urine acylglycines by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS): Reference intervals and disease specific patterns in individuals with organic acidemias and fatty acid oxidation disorders

Background: Acylglycine species accumulate in specific disorders of branched-chain amino acid metabolism and fatty acid beta-oxidation. These species are excreted in urine and their analysis can facilitate diagnosis. Previous studies evaluated reference ranges and increases in metabolic patients, but these involved small numbers of individuals. We have conducted an analysis encompassing large numbers of individuals to better characterize the reference ranges of these analytes and additionally describe our findings from patients with confirmed metabolic disorders. Methods: We conducted a retrospective analysis of approximately 9 y of urine acylglycine data from our clinical laboratory. Acylglycines were extracted from urine, derivatized and analyzed using UPLC-MS/MS. Reference ranges were determined from the non-diseased population. Data from confirmed patients were used to document the range of increases observed in these conditions and to generate multiple of the median graphs. Results: In total, 6162 urine specimens from 5633 patients with and without metabolic disorders were analyzed. Magnitude and pattern of acylglycine elevations in patients with confirmed metabolic disorders were documented. Conclusion: This manuscript extends our previously published method by providing the reference ranges and disease specific elevations and patterns of urine acylglycine species using the largest data set published to date.