Used in medical diagnostics and research to assess vitamin D status in the body. It serves as a reference standard in laboratory tests, particularly in immunoassays and liquid chromatography-mass spectrometry (LC-MS/MS), to accurately measure 25-hydroxyvitamin D levels in human serum or plasma. This helps in diagnosing and monitoring vitamin D deficiency, which is linked to bone disorders, immune dysfunction, and metabolic diseases. Also used in calibration of clinical instruments and in the development of diagnostic kits. Its standardized solution form ensures consistency and reliability in analytical measurements across healthcare and research settings.