Used as a stable isotope-labeled internal standard in mass spectrometry (MS) and liquid chromatography-mass spectrometry (LC-MS) assays for accurate quantification of endogenous cholic acid in biological samples such as plasma, serum, and urine. Its deuterated structure allows clear differentiation from natural cholic acid, minimizing interference from matrix components and improving measurement precision in metabolic studies. Commonly applied in research on bile acid metabolism, liver function, and gastrointestinal disorders. Also utilized in pharmacokinetic studies to track metabolic pathways and assess drug effects on bile acid homeostasis.