title: Influence of the immunoassay used in measurement of serum vitamin D levels.
abstract: BACKGROUND
  Serum 25-hydroxyvitamin D [25(OH)D] levels are the best indicator of vitamin D levels in the body. Precision, reproducibility, and lack of standardization are the main problems in such measurements. The aim of this study was to compare the 25(OH)D levels measured using Elecsys Vitamin D Total (Roche) and ADVIA Centaur Vitamin D Total (Siemens).
  
  
  METHODS
  25(OH)D levels were tested in 166 patients using both methods. Patients were subsequently divided into two groups: a «supplemented group» consisting of patients receiving vitamin D supplements, and an «untreated group» consisting of the rest of patients.
  
  
  RESULTS
  25(OH)D mean levels measured by the Roche and Siemens methods in the overall group were 33.6±16.0 and 19.8±12.4 ng/mL respectively. 54.2% of patients were receiving vitamin D supplements. In this group, mean 25(OH)D levels measured by the Roche and Siemens methods were 40.6±14.5 and 25.4±13.1 ng/mL respectively. In the untreated group, the respective values were 24.9±13.2 and 12.8±6.6 ng/mL. Prevalence of vitamin D deficiency (serum 25(OH)D levels less than 20 ng/mL) was higher in samples analyzed using the Siemens method (60.2%) as compared to those tested using the Roche method (23.5%).
  
  
  CONCLUSIONS
  The assays evaluated are not comparable to each other. Laboratory specialists should inform clinicians of the features of the method used for measuring 25(OH)D because this will have a direct impact on interpretation of the results and medical decisions.
authors.affiliation: Área de Diagnóstico Biológico, Hospital Universitario de la Ribera, Alzira, Valencia, España. Electronic address: silgopin@hotmail.com.
authors.forename: Silvia
authors.initials: S
authors.lastname: Górriz Pintado
authors.affiliation: Área de Diagnóstico Biológico, Hospital Universitario de la Ribera, Alzira, Valencia, España.
authors.forename: Pedro Luis
authors.initials: PL
authors.lastname: Estela Burriel
mesh_terms: D000368:Aged; D002112:Calcifediol / Q000097:blood* / Q000172:deficiency*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods; D008297:Male; D008875:Middle Aged; D014807:Vitamin D / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood / Q000175:diagnosis*
chemical_list: D014807:Vitamin D; D002112:Calcifediol
keywords: Comparación de métodos; Methods comparison; Roche; Siemens; Vitamin D; Vitamina D