title: Multicenter Comparison of Seven 25OH Vitamin D Automated Immunoassays.
abstract: BACKGROUND
  The measurement of 25OH vitamin D continues to grow in clinical laboratories. The aim of this multi-center study was to compare the results of seven automated commercial immunoassays with a reference HPLC technique.
  
  
  METHODS
  One hundred and twenty consecutive outpatient serum samples were centrifuged, divided in aliquots, frozen and shipped to the participating laboratories. 25OH Vitamin D was measured with a reference HPLC system and with seven automated commercial immunoassays (Roche Cobas E601, Beckman Coulter Unicel DXI 800, Ortho Vitros ES, DiaSorin Liaison, Siemens Advia Centaur, Abbott Architect i System and IDS iSYS).
  
  
  RESULTS
  Compared to the reference method, the regression coefficients ranged from 0.923 to 0.961 (all p<0.001). The slope of Deming fit ranged from 0.95 to 1.06, whereas the intercept was comprised between -15.2 and 9.2 nmol/L. The bias from the reference HPLC technique varied from -14.5 to 8.7 nmol/L. The minimum performance goal for bias was slightly exceeded by only one immunoassay. The agreement between HPLC and the different immunoassays at 50 nmol/L 25OH Vitamin D varied between 0.61 and 0.85 (all p<0.001). The percentage of samples below this cut-off was significantly different with only one immunoassay.
  
  
  CONCLUSIONS
  The excellent correlation with the reference HPLC technique attests that all seven automated immunoassays may be reliably used for routine assessment of 25OH-D in clinical laboratories. The significant bias among the different methods seems mostly attributable to the lack of standardization and calls for additional efforts for improving harmonization of 25OH-D immunoassays.
authors.affiliation: Laboratory of Clinical Chemistry and Hematology, Academic Hospital of Parma, Parma, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Lippi
authors.affiliation: Laboratory of Clinical Chemistry and Hematology, Academic Hospital of Verona, Verona, Italy.
authors.forename: Gian Luca
authors.initials: GL
authors.lastname: Salvagno
authors.affiliation: Laboratory of Clinical Chemistry and Hematology, San Bortolo Hospital, Vicenza, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Fortunato
authors.affiliation: Laboratory of Clinical Chemistry and Hematology, Academic Hospital of Parma, Parma, Italy.
authors.forename: Mariella
authors.initials: M
authors.lastname: Dipalo
authors.affiliation: Laboratory of Clinical Chemistry and Hematology, Academic Hospital of Parma, Parma, Italy.
authors.forename: Rosalia
authors.initials: R
authors.lastname: Aloe
authors.affiliation: Service of Laboratory Medicine, Hospital of Bassano del Grappa, Bassano del Grappa (VI), Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Da Rin
authors.affiliation: Laboratory of Clinical Chemistry and Hematology, San Bortolo Hospital, Vicenza, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Giavarina
keywords: 25OH-D; immunoassays; method comparison; standardization; vitamin D