title: Current 25-hydroxyvitamin D assays: do they pass the test?
abstract: BACKGROUND
  Vitamin D testing is becoming increasingly important with recent research demonstrating a correlation between vitamin D insufficiency and metabolic diseases, immunodeficiencies and other diseases. However, existing 25-hydroxyvitamin D (25OHD) assays lack comparability to the candidate reference method, causing difficulties in diagnosis and monitoring of vitamin D deficiency.
  
  
  METHODS
  We looked at the accuracy of 3 automated assays (Roche Diagnostics Elecsys® Total 25OHD assay, Abbott Architect® Total vitamin D assay, Advia Centaur® vitamin D Total assay) and Diasorin® Radioimmunoassay (RIA) compared to a routine laboratory Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS).
  
  
  RESULTS
  The correlation based on Passing Bablok regression was good with the slopes between 0.95 and 1.31 and the intercepts between -3.24 and 3.68. However, a significant positive bias was observed using the Abbott Architect and the Diasorin RIA. Using published analytical goals of coefficient of variation (CV) <10% and bias <5%, most methods did not meet these criteria. Using measurement of uncertainty of 9%, most methods were able to meet criteria using quality control materials but not patient samples.
  
  
  CONCLUSIONS
  Inadequacies of these assay performances are contributed by differences in method of extraction of vitamin D from vitamin D binding protein, cross-reactivities to 25OHD(2), 25OHD(3) and other vitamin D metabolites, matrix interferences and a lack of standardization.
authors.affiliation: Department of Laboratory Medicine, National University Hospital, Singapore 119074, Singapore. lizhen_ong@nuhs.edu.sg
authors.forename: Lizhen
authors.initials: L
authors.lastname: Ong
authors.forename: Sharon
authors.initials: S
authors.lastname: Saw
authors.forename: Noorulhijjah Bte
authors.initials: NB
authors.lastname: Sahabdeen
authors.forename: Kiat Teng
authors.initials: KT
authors.lastname: Tey
authors.forename: Chung Shun
authors.initials: CS
authors.lastname: Ho
authors.forename: Sunil Kumar
authors.initials: SK
authors.lastname: Sethi
mesh_terms: D002853:Chromatography, Liquid; D006801:Humans; D007118:Immunoassay; D008163:Luminescent Measurements / Q000592:standards*; D011786:Quality Control; D011863:Radioimmunoassay; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D053719:Tandem Mass Spectrometry; D035501:Uncertainty; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000175:diagnosis
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D