Used as a stable isotope-labeled internal standard in mass spectrometry (MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for accurate quantification of endogenous 17β-estradiol in biological samples such as serum, plasma, and urine. Its deuterium labels at positions 2,4,16,16,17 provide a distinct mass shift while maintaining nearly identical chemical and chromatographic behavior to the unlabeled compound, ensuring high precision in hormone testing. Commonly applied in clinical diagnostics, endocrinology research, and pharmacokinetic studies to measure estrogen levels with minimal interference from matrix effects.