title: Relative importance of the determinants of serum levels of 25-hydroxy vitamin D in patients with chronic kidney disease.
abstract: BACKGROUND
  The cause of vitamin D deficiency in chronic kidney disease (CKD) is probably multi-factorial; however, the relative importance of each potential determinant is uncertain.
  
  
  OBJECTIVE
  To determine factors associated with serum levels of 25-hydroxy vitamin D (25OHD) and their relative importance in a cohort of pre-dialysis CKD patients.
  
  
  METHODS
  Incident patients admitted to a CKD outpatient clinic were included. Those who were receiving vitamin D supplements or anticonvulsants were excluded. In addition to demographic and clinical data, information about outdoor physical activity, season of blood collection, prescription of statins, anti-angiotensin drugs and xanthine-oxidase inhibitors were included as potential determinants. Johnson's relative weights analysis was used to estimate the relative importance of each potential determinant and the results were expressed as percentage contribution to multiple R.
  
  
  RESULTS
  The study group consisted of 397 patients, 30 of whom were excluded. The mean serum level of 25OHD was 13.7±7.4ng/ml, and 81% of patients had serum levels lower than 20ng/ml. By multiple linear regression and relative weights analyses, the best determinants of low serum 25OHD levels and their relative importance were: higher proteinuria (28.5%), old age (21.4%), low physical activity (19.4%), female gender (19.3%) and low serum bicarbonate levels (11.4%).
  
  
  CONCLUSIONS
  Proteinuria and age are the determinants with the highest relative importance for predicting 25OHD levels in CKD patients.
authors.affiliation: Servicio de Nefrología, Hospital Ramón y Cajal, Madrid, España. Electronic address: fcaravacaf@gmail.com.
authors.forename: Fernando
authors.initials: F
authors.lastname: Caravaca-Fontán
authors.affiliation: Servicio de Nefrología, Hospital Infanta Cristina, Badajoz, España.
authors.forename: Boris
authors.initials: B
authors.lastname: Gonzales-Candia
authors.affiliation: Servicio de Nefrología, Hospital Infanta Cristina, Badajoz, España.
authors.forename: Enrique
authors.initials: E
authors.lastname: Luna
authors.affiliation: Servicio de Nefrología, Hospital Infanta Cristina, Badajoz, España.
authors.forename: Francisco
authors.initials: F
authors.lastname: Caravaca
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002112:Calcifediol / Q000097:blood*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D051436:Renal Insufficiency, Chronic / Q000097:blood* / Q000150:complications; D014808:Vitamin D Deficiency / Q000453:epidemiology*
chemical_list: D002112:Calcifediol
keywords: 25-hidroxi-colecalciferol; 25-hydroxy vitamin D; Chronic kidney disease; Enfermedad renal crónica; Proteinuria