Automated Competitive Protein-Binding Assay for Total 25-OH Vitamin D, Multicenter Evaluation and Practical Performance.

Background The Roche Elecsys Vitamin D Total competitive protein-binding assay uses recombinant vitamin D binding protein for measuring 25-hydroxyvitamin D (25-OHD), which is different from commonly used antibody assays. Methods The assay, standardized against LC-MS/MS, was tested at four sites. Evaluation included precision; between-laboratory variability; functional sensitivity; correlation to LC-MS/MS, HPLC, and immunoassays; as well as robustness, traceability, and EQAS performance. Results Precision testing showed within-run coefficient of variations (CVs) of ≤7%, within-laboratory CVs of <9.5%, between-laboratory precision CVs of ≤10.1%, and a functional sensitivity below 9.8 nmol/l (at CV 12.9%). The assay showed equivalent 25-OHD levels for matched serum and plasma samples, good reagent lot-to-lot consistency in pooled sera over time, and good agreement with HPLC (relative bias −8.8%). Comparison with LC-MS/MS methods yielded relative biases of −15.4, −13.5, −10.2, and 3.2%. Comparison against immunoassays showed a relative bias of 14.5% (DiaSorin Liaison) and −58.2% (IDS-iSYS). The overall mean results in 2 years DEQAS was 102% of the ALTM. In a certified reference patient panel, the average bias was <4% for the sum of 25-OHD2 and 25-OHD3. Conclusion The Elecsys Vitamin D Total assay demonstrated good overall performance and is, according to present standards, very suitable for automated measurement of 25-OHD.