State-of-the-art vitamin D assays: a comparison of automated immunoassays with liquid chromatography-tandem mass spectrometry methods.
BACKGROUND
Vitamin D testing is increasing worldwide. Recently several diagnostic manufacturers including Abbott and Siemens have launched automated 25-hydroxy vitamin D (25OH-D) immunoassays. Furthermore, preexisting assays from DiaSorin and Roche have recently been modified. We compared the performance of 5 automated immunoassays, an RIA and 2 liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods.


METHODS
Aliquots of 170 randomly selected patient samples were prepared and 25OH-D was measured by 2 LC-MS/MS methods, an RIA (DiaSorin), and automated immunoassays from Abbott (Architect), DiaSorin (LIAISON), IDS (ISYS), Roche (E170, monoclonal 25OH-D(3) assay), and Siemens (Centaur). Within-run and between-run imprecision were evaluated by measurement of 5 replicates of 2 serum pools on 5 consecutive days.


RESULTS
The LC-MS/MS methods agreed, with a concordance correlation coefficient (CCC) of 0.99 and bias of 0.56 μg/L (1.4 nmol/L). The RIA assay showed a performance comparable to LC-MS/MS, with a CCC of 0.97 and a mean bias of 1.1 μg/L (2.7 nmo/L). All immunoassays measured total 25OH-D (including D(3) and D(2)), with the exception of the Roche assay (D(3) only). Among the immunoassays detecting total 25OH-D, the CCCs varied between 0.85 (Abbott) to 0.95 (LIAISON). The mean bias ranged between 0.2 μg/L (0.5 nmol/L) (LIAISON) and 4.56 μg/L (11.4 nmol/L) (Abbott). The Roche 25OH-D(3) assay demonstrated small mean bias [-2.7 μg/L (-6.7 nmol/L)] [-2.7 μg/L (-6.7 nmol/L)] but a low CCC of just 0.66. Most assays demonstrated good intra- and interassay precision, with CV <10%.


CONCLUSIONS
Automated immunoassays demonstrated variable performance and not all tests met our minimum performance goals. It is important that laboratories be aware of the limitations of their assay.
Laverty Pathology, North Ryde, New South Wales, Australia.
Christopher-John L
CJ
Farrell
Steven
S
Martin
Brett
B
McWhinney
Isabella
I
Straub
Paul
P
Williams
Markus
M
Herrmann
D001331:Automation; D002853:Chromatography, Liquid; D006801:Humans; D007118:Immunoassay; D012680:Sensitivity and Specificity; D053719:Tandem Mass Spectrometry; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
D014807:Vitamin D; C104450:25-hydroxyvitamin D