title: Critically Ill Children Have Low Vitamin D-Binding Protein, Influencing Bioavailability of Vitamin D.
abstract: BACKGROUND
  Vitamin D deficiency, often defined by total serum 25-hydroxyvitamin D (25[OH]D) <20 ng/ml, is common in critically ill patients, with associations with increased mortality and morbidity in the intensive care unit. Correction of vitamin D deficiency in critical illness has been recommended, and ongoing clinical trials are investigating the effect of repletion on patient outcome. The biologically active amount of 25(OH)D depends on the concentration and protein isoform of vitamin D-binding protein (VDBP), which is also an acute-phase reactant affected by inflammation and injury.
  
  
  OBJECTIVE
  We performed a secondary analysis of a cohort of critically ill children in which we reported a high rate of vitamin D deficiency, to examine how VDBP level and genotype would impact vitamin D status.
  
  
  METHODS
  We prospectively enrolled 511 children admitted to the pediatric intensive care unit over a 12-month period.
  
  
  RESULTS
  We measured serum VDBP in 479 children. We genotyped single nucleotide polymorphisms rs7041 and rs4588 in the VDBP gene (GC) to determine haplotypes GC1F, GC1S, and GC2 in 178 subjects who consented, then calculated bioavailable 25(OH)D from serum 25(OH)D, VDBP, albumin, and GC haplotype. The median serum VDBP level was 159 μg/ml (interquartile range, 108-221), lower than has been reported in healthy children. Factors predicting lower levels in multivariate analysis included age <1 year, nonwhite race, being previously healthy, 25(OH)D <20 ng/ml and greater illness severity. In the subgroup that was genotyped, GC haplotype had the strongest association with VDBP level; carriage of one additional copy of GC1S was associated with a 37.5% higher level (95% confidence interval, 31.9-44.8; P < 0.001). Bioavailable 25(OH)D was also inversely associated with illness severity (r = -0.24, P < 0.001), and ratio to measured total 25(OH)D was variable and related to haplotype.
  
  
  CONCLUSIONS
  Physiologic deficiency of 25(OH)D in critical illness may be more difficult to diagnose, given that lower VDBP levels increase bioavailability. Treatment studies conducted on the basis of total 25(OH)D level, without consideration of VDBP concentration and genotype, may increase the risk of falsely negative results.
authors.affiliation: 1 Department of Anesthesia, Perioperative and Pain Medicine, Division of Critical Care Medicine.|2 Department of Anaesthesia and.
authors.forename: Kate
authors.initials: K
authors.lastname: Madden
authors.affiliation: 3 Division of Endocrinology, and.|4 the Clinical Research Center, Boston Children's Hospital, Boston, Massachusetts.|5 Department of Pediatrics, Harvard Medical School, Boston, Massachusetts.
authors.forename: Henry A
authors.initials: HA
authors.lastname: Feldman
authors.affiliation: 6 Department of Orthopaedics, University of California at Los Angeles, Los Angeles, California.
authors.forename: Rene F
authors.initials: RF
authors.lastname: Chun
authors.affiliation: 7 Nutrition and Health Sciences Program, Laney Graduate School, Emory University, Atlanta, Georgia.
authors.forename: Ellen M
authors.initials: EM
authors.lastname: Smith
authors.affiliation: 1 Department of Anesthesia, Perioperative and Pain Medicine, Division of Critical Care Medicine.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Sullivan
authors.affiliation: 1 Department of Anesthesia, Perioperative and Pain Medicine, Division of Critical Care Medicine.
authors.forename: Anna A
authors.initials: AA
authors.lastname: Agan
authors.affiliation: 8 Drexel School of Medicine, Philadelphia, Pennsylvania; and.
authors.forename: Shannon M
authors.initials: SM
authors.lastname: Keisling
authors.affiliation: 9 Department of Pediatrics, University of Minnesota, Minneapolis, Minnesota.
authors.forename: Angela
authors.initials: A
authors.lastname: Panoskaltsis-Mortari
authors.affiliation: 1 Department of Anesthesia, Perioperative and Pain Medicine, Division of Critical Care Medicine.|2 Department of Anaesthesia and.
authors.forename: Adrienne G
authors.initials: AG
authors.lastname: Randolph
mesh_terms: D000293:Adolescent; D000328:Adult; D001682:Biological Availability; D002648:Child; D002675:Child, Preschool; D016638:Critical Illness / Q000628:therapy*; D005260:Female; D006239:Haplotypes; D006801:Humans; D007223:Infant; D008297:Male; D020641:Polymorphism, Single Nucleotide; D011446:Prospective Studies; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000175:diagnosis*; D014809:Vitamin D-Binding Protein / Q000097:blood* / Q000235:genetics*; D055815:Young Adult
chemical_list: D014809:Vitamin D-Binding Protein; D014807:Vitamin D; C104450:25-hydroxyvitamin D
keywords: bioavailability; critical illness; haplotype; vitamin D; vitamin D–binding protein