The Measurement of 3-Epimer 25-Hydroxyvitamin D by Mass Spectrometry in Clinical Specimens Detects Inconsequential Levels in Adult Subjects

BackgroundVitamin D is derived from dietary sources or from the action of ultraviolet light on 7-dehydrocholesterol and undergoes a number of enzymatic modifications that lead to the synthesis of active vitamin D metabolites or metabolites with reduced biological activity. Among these, epimerization at the 3-hydroxyl group leads to the synthesis of 3-epimer 25-hydroxyvitamin D (3EVD). Described first in biological system experiments using in vitro incubation of vitamin D in cell culture, this molecule has been reported as having distinct activities when compared with 25-hydroxy vitamin D (25OHVD). Measurements of vitamin D have been conducted using a variety of methodologies and have led to conflicting assessments of the quantities of 3EVD3 that are measured.MethodThe present article describes the development and use of a simple liquid chromatography–tandem mass spectrometry method validated by the Clinical Laboratory Improvement Amendments to quantitate 3EVD3 in 3528 subjects, including 309 children (162 are