Measurement of serum uric acid by isotope dilution liquid chromatography tandem mass spectrometry: Modification of a candidate reference measurement method and its clinical application

Uric acid is a precipitating factor for gout and renal disease, and regular monitoring of uric acid concentration is essential for health management. Hence, accurate measurement is indispensable for clinical diagnosis. Reference measurement procedure (RMP) is an essential element to ensure accuracy and comparability of tested results. In this study, the optimization of a candidate RMP (cRMP) adopting isotope dilution coupled with liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) method for human serum uric acid measurement has been developed. The accuracy of this cRMP was validated by measuring certified reference materials (CRMs) and participating in the external quality assessment (EQA) scheme initiated by International Federation of Clinical Chemistry (IFCC) and National Center for Clinical Laboratory (NCCL). Biases were −0.64-1.51%, which were within the required equivalent limit. Excellent precision was obtained with intra- and inter-assay CVs of 0.42–0.73% and 0.20–0.43%, respectively. The limit of detection (LOD) and limit of quantification (LOQ) was determined to be 0.24 and 1.19 μmol/L, respectively. A good liner response was obtained ranged from 30.0 to 895 μmol/L. Compared with the previous RMP for uric acid, the much easier one-step protein precipitation method without further evaporation, the simplified isocratic elution of chromatographic separation condition, and the shorter analysis running time in only 5 min allowed simpler and faster analysis. Moreover, this optimized cRMP was also applied for value assignment for clinical serum samples covered a wide concentration range of uric acid and obtained a decent calibration and measurement capability (CMC).