title: Incident isolated 1,25(OH)(2)D(3) deficiency is more common than 25(OH)D deficiency in CKD.
abstract: BACKGROUND
  Vitamin D deficiencies are well described in general populations and in those with chronic kidney disease (CKD). Although serum 25(OH)D may be a good indicator of vitamin D status in healthy individuals, the hydroxylated product, 1,25(OH)(2)D, essential for important biological functions such as mineral metabolism, bone turnover, regulation of protein synthesis, cell differentiation and proliferation may be a more suitable indicator for individuals with CKD.
  
  
  METHODS
  We report an observational prospective cohort study of the incidence after 12 months of new isolated 1,25(OH)(2)D and new 25(OH)D deficiency in CKD patients (estimated glomerular filtration rate [eGFR] <60 ml/min), who were vitamin D replete at baseline. All analyses were run in a central laboratory.
  
  
  RESULTS
  Of 1,256 patients who completed the study at 12 months, 631 were replete in both 25(OH)D and 1,25(OH)(2)D at baseline; at 12 months, 65% remained replete, 25% developed an isolated 1,25(OH)(2)D deficiency, whereas only 6% developed an isolated 25(OH)D deficiency. Based on the multinomial logistic regression model, factors that were associated with 12-month changes in vitamin D status were diabetes, baseline values of eGFR, albumin and both 25(OH)D and 1,25(OH)(2)D (all p values <0.03). Patients with diabetes, lower albumin, lower eGFR, lower levels of 25(OH)D and 1,25(OH)(2)D at baseline were at increased risk of developing isolated 1,25(OH)(2)D deficiency.
  
  
  CONCLUSIONS
  The high incidence of new isolated 1,25(OH)(2)D deficiency as compared with new 25(OH)D deficiency, in the presence of 25(OH)D sufficiency, brings into question the value of measuring 25(OH)D levels in CKD. The significance of these findings and implications for replacement strategies require further study.
authors.affiliation: BC Provincial Renal Agency, Vancouver, British Columbia, Canada. alevin@providencehealth.bc.ca
authors.forename: Adeera
authors.initials: A
authors.lastname: Levin
authors.forename: Melina
authors.initials: M
authors.lastname: Le Barbier
authors.forename: Lee
authors.initials: L
authors.lastname: Er
authors.forename: Dennis
authors.initials: D
authors.lastname: Andress
authors.forename: Mhairi K
authors.initials: MK
authors.lastname: Sigrist
authors.forename: Ognjenka
authors.initials: O
authors.lastname: Djurdjev
mesh_terms: D000368:Aged; D002117:Calcitriol / Q000172:deficiency*; D002908:Chronic Disease; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007674:Kidney Diseases / Q000097:blood*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood* / Q000503:physiopathology
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D; D002117:Calcitriol