Used as a stable isotope-labeled internal standard in mass spectrometry for quantitative analysis of urea in biological samples such as blood, plasma, and urine. Its deuterated structure allows clear differentiation from non-labeled urea, improving accuracy in metabolic studies and clinical diagnostics. Also employed in research on nitrogen metabolism and protein breakdown, where tracking urea production and excretion is essential. Due to its high isotopic purity, it supports precise calibration in analytical methods and helps minimize matrix effects in liquid chromatography-tandem mass spectrometry (LC-MS/MS) workflows.