title: Relationship between serum 25-hydroxyvitamin D and parathyroid hormone in the search for a biochemical definition of vitamin D deficiency in children.
abstract: BACKGROUND
  Current guidelines use differing definitions of vitamin D deficiency based on serum 25-hydroxyvitamin D (25OHD) levels, which complicates clinical decision making on vitamin D doses used for the prevention and treatment. This study examined the natural relationship between serum 25OHD, parathyroid hormone (PTH), calcium, phosphate, and alkaline phosphatase.
  
  
  METHODS
  Two-hundred and fourteen children routinely admitted without conditions affecting the natural relationship among metabolites, including 17 with radiologically confirmed vitamin D deficiency rickets, were studied. The frequency of abnormal bone metabolites was examined for different 25OHD thresholds.
  
  
  RESULTS
  The best fitting intersection point where PTH levels increased was a 25OHD level of 34 nmol/l (R(2) = 0.454; 95% confidence interval: 27-41 nmol/l). Seventy-three and 86% of the children demonstrated some biochemical abnormality below 25OHD levels of 41 and 27 nmol/l, respectively. All patients with rickets had 25OHD levels < 34 nmol/l. The vast majority of children with abnormal bone metabolites had 25OHD levels < 34 nmol/l and PTH levels > 50 ng/l.
  
  
  CONCLUSIONS
  Vitamin D deficiency, based on PTH elevation, was best defined by a 25OHD level of < 34 nmol/l. Because deficient calcium supply often coexists with vitamin D deficiency and both can independently cause nutritional rickets, a threshold for the skeletal effects of vitamin D should not be based purely on 25OHD levels.
authors.affiliation: Department of Endocrinology and Diabetes, Birmingham Children's Hospital, Birmingham, UK.
authors.forename: Navoda
authors.initials: N
authors.lastname: Atapattu
authors.forename: Nick
authors.initials: N
authors.lastname: Shaw
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Högler
mesh_terms: D000469:Alkaline Phosphatase / Q000097:blood; D001842:Bone and Bones / Q000378:metabolism*; D002118:Calcium / Q000097:blood; D002648:Child; D004739:England; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D010281:Parathyroid Hormone / Q000097:blood*; D010710:Phosphates / Q000097:blood; D012015:Reference Standards; D012279:Rickets / Q000097:blood*; D018709:Statistics, Nonparametric; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000175:diagnosis*
chemical_list: D010281:Parathyroid Hormone; D010710:Phosphates; D014807:Vitamin D; C104450:25-hydroxyvitamin D; D000469:Alkaline Phosphatase; D002118:Calcium