Evaluation and clinical application of an accurate isotope dilution liquid chromatography-tandem mass spectrometry method for serum glycocholic acid.

Glycocholic acid (GCA) is an important identified biomarker for various hepatobiliary diseases. Accurate measurement of GCA is essential for diagnosis and treatment of hepatobiliary diseases. Our aim was to develop and validate a high accuracy method for the quantification of GCA in serum. An isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC/MS/MS) method has been developed and validated. The assay validation was performed, including imprecision, trueness, matrix effects, linearity, interference, and carry-over, etc. Furthermore, the developed method was applied to comparison with three latex-enhanced immunoturbidimetric assays and for external quality assessment (EQA) of clinical systems. Excellent linearity coefficients (R2 = 0.9998) were obtained in the range from 0.063 to 49.53 μg/g. The limit of detection and limit of quantification were 0.1 ng/mL and 2.3 ng/mL, respectively. The total imprecisions were below 2.33% for low, medium, and high concentration samples. Good recoveries were achieved at three spiked levels (98.94% - 101.80%), and a relative expanded uncertainty was < 3% (k = 2). No interference, matrix effects, or carry-over were observed. Significant bias across routine GCA assays obtained by immunoassays and ID-LC/MS/MS method highlighted the urgency of standardization for the measurement of GCA. This study successfully established an accurate quantitative method for detecting serum GCA using ID-LC/MS/MS. The method could serve as an accurate reference baseline for routine methods and can be used for value assignment for reference materials. It could support EQA management for GCA testing and promote GCA standardization.