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 vitaminD(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 mu g/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 mu g/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 mu g/L (0.5 nmol/L) (LIAISON) and 4.56 mu g/L (11.4 nmol/L) (Abbott). The Roche 25OH-D-3 assay demonstrated small mean bias [-2.7 mu g/L (-6.7 nmol/L)] [-2.7 mu g/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. (C) 2011 American Association for Clinical Chemistry