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

Abstract

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 DE-QAS 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.

A comparison between two different automated total 25-hydroxyvitamin D immunoassay methods using liquid chromatography-tandem mass spectrometry

“…In this study, the Roche Cobas Vitamin D total assay method showed a bias of -14.1%. Previous studies evaluating the Cobas methods found negative bias compared to that of LC-MS/MS, which was similar to the results of our study ( 24 , 25 ).…”

Looking beyond linear regression and Bland-Altman plots: a comparison of the clinical performance of 25-hydroxyvitamin D tests

“…The Bland-Altman analyses revealed small ( < 10%) biases in many comparisons, but the limits of agreement were unacceptably wide in all cases. These findings are similar to those observed by others when these assays were compared to reference methods [28][29][30].…”

Vitamin D status and functional parameters: A cross-sectional study in an older population

“…In relation to the laboratory analysis of serum 25(OH)D, the Vitamin D External Quality Assessment Scheme has revealed method-related differences in 25-(OH)D results, raising concerns about the comparability and accuracy of different assays [ 71 , 72 ]. The competitive protein binding assay used in the present study was reported as very suitable for automated measurement of 25(OH)D [ 73 ], however, a potential overestimative of values should also not be ruled out [ 73 ]. Considering this fact, the low 25(OH)D levels found in the present study may be even more concerning, but it is not expected that the direction or strength of the observed associations are affected, since it reflects in a systematic overestimation.…”