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.
Uvod: Merenje 25OH vitamina D sve se češće obavlja u kliničkim laboratorijama. Cilj ove multicentrične studije bio je da se rezultati sedam automatizovanih komercijalnih imunoeseja uporede sa referentnom tehnikom HPLC.
Metode: Sto dvadeset uzoraka seruma od uzastopnih pacijenata koji su posetili kliniku centrifugirano je, podeljeno u alikvote, smrznuto i poslato laboratorijama koje su učestvovale u istraživanju. Nivo 25OH vitamina D meren je pomoću referentnog sistema HPLC i pomoću sedam automatizovanih komercijalnih imunoeseja (Roche Cobas E601, Beckman Coulter Unicel DXI 800, Ortho Vitros ES, DiaSorin Liaison, Siemens Advia Centaur, Abbott Architect i System i IDS iSYS).
Rezultati: U poređenju sa referentnim metodom, koeficijenti regresije kretali su se između 0,923 i 0,961 (svuda p<0,001). Nagib za Demingovu regresiju kretao se od 0,95 do 1,06, dok je kriva obuhvatila područje između −15,2 i 9,2 nmol/L. Odstupanje od referentne tehnike HPLC kretalo se od −14,5 do 8,7 nmol/L. Minimalni domet za odstupanje blago je prešao samo jedan imunoesej. Slaganje između HPLC i različitih imunoeseja pri koncentraciji od 50 nmol/L 25OH vitamina D variralo je između 0,61 i 0,85 (svuda p<0,001). Procenat uzoraka ispod ove cut-off vrednosti značajno se razlikovao samo za jedan imunoesej.
Zaključak: Odlična korelacija sa referentnom tehnikom HPLC potvrđuje da se svih sedam automatizovanih imunoeseja mogu sa sigurnošću koristiti za rutinsko određivanje nivoa 25OH-D u kliničkim laboratorijama. Značajno odstupanje između različitih metoda po svoj prilici se može uglavnom pripisati nedostatku standardizacije i zahteva dodatne napore kako bi se popravila harmonizacija imunoeseja za 25OH-D.
Keywords: 25OH-D; immunoassays; method comparison; standardization; vitamin D.