The measurement of 3-epimer 25-hydroxyvitamin D by mass spectrometry in clinical specimens detects inconsequential levels in adult subjects.

BACKGROUND: Vitamin 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. METHOD: The 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 <2 years) and 232 pregnant women. RESULTS: Our findings demonstrate that, although 3EVD3 constitutes a significant proportion of measureable 25OHVD3 in subjects younger than 1 year, 3EVD3 levels are negligible in most subjects older than 1 year. CONCLUSIONS: It is important to choose the correct 25OHVD assay dependent on the age of the patient. Patients younger than 1 year should be run on a liquid chromatography-tandem mass spectrometry assay proven to not have potential contributions from any 3EVD present in the sample.