Used in medical diagnostics and research to assess vitamin D status in the body. It serves as a reference standard in laboratory tests that measure 25-hydroxyvitamin D levels in blood, helping to diagnose deficiencies or monitor supplementation. Commonly used in immunoassays and chromatography methods for accurate quantification. Also utilized in calibration of analytical instruments and development of diagnostic kits. Supports studies on bone health, calcium metabolism, immune function, and chronic disease research.