title: Automated Competitive Protein-Binding Assay for Total 25-OH Vitamin D, Multicenter Evaluation and Practical Performance.
abstract: BACKGROUND
  The Roche Elecsys Vitamin D Total competitive protein-binding assay uses recombinant vitamin D binding protein for measuring 25-hydroxyvitamin D (25-OHD), which is different from commonly used antibody assays.
  
  
  METHODS
  The assay, standardized against LC-MS/MS, was tested at four sites. Evaluation included precision; between-laboratory variability; functional sensitivity; correlation to LC-MS/MS, HPLC, and immunoassays; as well as robustness, traceability, and EQAS performance.
  
  
  RESULTS
  Precision testing showed within-run coefficient of variations (CVs) of ≤ 7%, within-laboratory CVs of <9.5%, between-laboratory precision CVs of ≤ 10.1%, and a functional sensitivity below 9.8 nmol/l (at CV 12.9%). The assay showed equivalent 25-OHD levels for matched serum and plasma samples, good reagent lot-to-lot consistency in pooled sera over time, and good agreement with HPLC (relative bias -8.8%). Comparison with LC-MS/MS methods yielded relative biases of -15.4, -13.5, -10.2, and 3.2%. Comparison against immunoassays showed a relative bias of 14.5% (DiaSorin Liaison) and -58.2% (IDS-iSYS). The overall mean results in 2 years DEQAS was 102% of the ALTM. In a certified reference patient panel, the average bias was < 4% for the sum of 25-OHD2 and 25-OHD3.
  
  
  CONCLUSIONS
  The Elecsys Vitamin D Total assay demonstrated good overall performance and is, according to present standards, very suitable for automated measurement of 25-OHD.
authors.affiliation: Meander Medisch Centrum, Amersfoort, The Netherlands.
authors.forename: Jos P M
authors.initials: JP
authors.lastname: Wielders
authors.affiliation: Healthscope Pathology, Clayton, Victoria, Australia.
authors.forename: Graeme F
authors.initials: GF
authors.lastname: Carter
authors.affiliation: Roche Diagnostics GmbH, Penzberg, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Eberl
authors.affiliation: Southern IML Pathology, Wollongong, New South Wales, Australia.
authors.forename: Gary
authors.initials: G
authors.lastname: Morris
authors.affiliation: Limbach Laboratories, Heidelberg, Germany.
authors.forename: Heinz Jürgen
authors.initials: HJ
authors.lastname: Roth
authors.affiliation: Roche Diagnostics GmbH, Penzberg, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Vogl
mesh_terms: D015652:25-Hydroxyvitamin D 2 / Q000378:metabolism*; D001331:Automation; D001667:Binding, Competitive; D001774:Blood Chemical Analysis / Q000592:standards*; D002853:Chromatography, Liquid / Q000379:methods; D003955:Diagnostic Tests, Routine / Q000592:standards*; D006801:Humans; D011485:Protein Binding; D053719:Tandem Mass Spectrometry / Q000379:methods; D014809:Vitamin D-Binding Protein / Q000378:metabolism*
chemical_list: D014809:Vitamin D-Binding Protein; D015652:25-Hydroxyvitamin D 2
keywords: 25-hydroxyvitamin D; Elecsys vitamin D total; VDBP; electrochemiluminescence; robustness; vitamin D; vitamin D binding protein