Measured free 25-hydroxyvitamin D in healthy children and relationship to total 25-hydroxyvitamin D, calculated free 25-hydroxyvitamin D and vitamin D binding protein

Maria Lopez-Molina, Cecilia Santillan, Marta Murillo, Aina Valls, Laura Bosch, Joan Bel, María Luisa Granada

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20 Citations (Scopus)

Abstract

© 2018 The Canadian Society of Clinical Chemists Background: vitamin D deficiency in children is still a global health problem. Measuring free 25-hydroxyvitamin D concentrations could provide a better estimate of the vitamin D status than total 25-hydroxyvitamin D (25(OH)D) levels. Objective: To assess the relationship between measured free vitamin D (m-f25(OH)D) and calculated free 25(OH)D (c-f25(OH)D), total 25(OH)D, intact parathyroid hormone (iPTH) and other markers of phosphocalcic metabolism. To establish serum m-f25(OH)D concentrations corresponding to a total 25(OH)D > 50 nmol/L which is accepted as vitamin D-sufficiency status in children. Design: Prospective cohort study. Setting: January and February 2017 in a Mediterranean population. Patients: healthy children. Measurements: m-f25(OH)D and vitamin D binding protein (VDBP) by ELISA. Free 25(OH)D was calculated using the formula described by Bikle. Results: m-f25(OH)D directly correlated with total 25(OH)D (r:0.804,p <.001), serum calcium (r:0.26,p:0.035), and c-f25(OH)D (r:0.553,p:0.016); and inversely with iPTH (r:-0.374, p:0.002), alkaline phosphatase (r:-0.28, p:0.026), and age (r:-0.289, p:0.018). Total 25(OH)D correlated with the same parameters as m-f25(OH)D except for serum calcium. However, c-f25(OH)D correlated only with total 25(OH)D and VDBP, both included in the calculation formula. Multiple regression analysis showed that m-f25(OH)D variations were independently explained by calcium (β:0.156, p:0.026) and total 25(OH)D (β:0.043, p <.001). The optimal m-f25(OH)D cut-off for discriminating between insufficient and sufficient total 25(OH)D was >9.8 pmol/L (Area Under Curve (AUC): 0.897 (95% confidence interval (CI): (0.798–0.958); p <.001; sensitivity:72.7% (95%CI: 49.8–89.3); specificity: 95.5% (95%CI: 84.5–99.4)). Conclusions: Directly measured free vitamin D correlated better with markers of phosphocalcic metabolism than total 25(OH)D and c-f25(OH)D in a population of healthy children.
Original languageEnglish
Pages (from-to)23-27
JournalClinical Biochemistry
Volume61
DOIs
Publication statusPublished - 1 Nov 2018

Keywords

  • 25-Hydroxyvitamin D
  • Children
  • Free 25-hydroxyvitamin D
  • Vitamin D binding protein
  • Vitamin D insufficiency

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