Evaluation of new Beckman Coulter 25(OH) Vitamin D assay and potential improvement of clinical interpretation

INTRODUCTION: The aim of this study was to assess the analytical performances of the newly developed Access2 25-hydroxyvitamin D (25(OH)D) total immunoassay on two analysers, DxI800 and Access2 (Beckman Coulter, Brea, CA, USA), and compare these two and a recalibrated Modular E 170 25(OH)D assay (Roche Diagnostics, Penzberg, Germany) with reference liquid chromatography tandem-mass spectrometry (LC-MS/MS) with special emphasis on clinical diagnosis. MATERIALS AND METHODS: Beckman immunoassays were assessed for imprecision, accuracy, limit of blank (LoB), limit of detection (LoD), limit of quantitation (LoQ), linearity, interference, and carryover. One hundred and nineteen samples were run on DxI 800, Access2, and E 170, and agreement with the LC-MS/MS method was evaluated. RESULTS: DxI 800 and Access2 assays showed good performances in terms of LoB, LoD, LoQ, linearity, and interference. All immunoassays showed negative biases ranging from - 8.6% (DxI 800) to - 19.2% (Access2). DxI 800 and Access2 systems had proportional biases, and the E170 system had a constant bias with the largest random error. Concordance correlation coefficient values ranged from 0.941 (CI: 0.917-0.958) for DxI800 to 0.854 (CI: 0.811-0.889) for Access2. Kappa (κ) coefficients were found moderate for Dxl (0.709; CI: 0.581-0.837) and E170 (0.771; CI: 0.587-0.844) and fair for Access2 (0.572; CI: 0.428-0.716). CONCLUSIONS: All immunoassays can be used in routine 25(OH)D measurements, still fairly diagnosing patients' status. Recent standardization attempts seem not to contribute too much to clinical diagnosis. A clinical laboratory must at least be aware of its method to avoid misinterpretation of results.