The Body Needs All Forms of Vitamin D - GrassrootsHealth
Standardized measurement of circulating vitamin D [25(OH)D] and its putative role as a serum biomarker in Alzheimer's disease and Parkinson's disease - ScienceDirect
Using gas chromatography and mass spectrometry to determine 25-hydroxy" by M.-Y. Yang, C.-Y. Huang et al.
Vitamin D Tests - My Endo Consult
25-OH Vitamin D3/D2 RP-HPLC Kit - Immundiagnostik, Inc.
Vitamin D deficiency: Is it really a problem - and what's the solution? | Society for Endocrinology