• Moon Jeong Lee, Malcolm D Kearns, Ellen M Smith, Li Hao, Thomas R Ziegler, Jessica A Alvarez, and Vin Tangpricha.
• Division of Endocrinology, Metabolism and Lipids (MJL, MDK, LH, TRZ, JAA, VT), Department of Medicine, Emory University, Atlanta, Georgia; Nutrition and Health Sciences Program (EMS, VT), Laney Graduate School, Emory University, Atlanta, Georgia; Atlanta Veterans Affairs Medical Center (VT), Section of Endocrinology, Atlanta, Georgia.
• Am. J. Med. Sci. 2015 Nov 1; 350 (5): 374379374-9.

BackgroundVitamin D deficiency is common in cystic fibrosis (CF), but there is no previous data on free 25-hydroxyvitamin D (25[OH]D) in CF or in relation to healthy individuals.MethodsWe assessed total serum 25(OH)D concentration by chemiluminescence and serum free 25(OH)D concentration by both direct measurement (ELISA) and calculation, using serum albumin and vitamin D binding protein (VDBP) levels in 80 subjects (28 healthy adults, 25 clinically stable adults and children with CF and 27 adults experiencing a CF exacerbation).ResultsSerum albumin and VDBP concentrations were lower in CF compared with healthy controls. Total serum 25(OH)D concentrations were positively correlated with both calculated and measured free 25(OH)D (P < 0.001 for both). Calculated and directly measured serum free 25(OH)D levels were positively correlated (P < 0.001).ConclusionsSerum levels of directly measured free 25(OH)D positively correlated with total 25(OH)D, suggesting that achieving sufficient total serum 25(OH)D may result in adequate free 25(OH)D levels in CF.

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