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.