Two-site evaluation of the Roche Elecsys Vitamin D total III assay

The high request for vitamin D testing in the last decades has led manufacturers to develop assays on automated immunoassay platforms. The objective of this study was to evaluate the performance of the new Elecsys Vitamin D total III assay for the measurement of total 25(OH)D.

A total of 844 serum samples collected in two clinical laboratories were used to evaluate the new Roche Elecsys Vitamin D total III assay. Comparisons with Roche Elecsys Vitamin D total II and liquid chromatography tandem mass spectrometry (LC-MS/MS) were carried out. Additionally, assay imprecision, linearity, matrix effects, biotin interference, cross-reactivity with 24,25(OH)₂D₃ and 3-epi-25(OH)D₃, and outlier rate were evaluated for the Elecsys Vitamin D total III assay.

Only the comparison between LC-MS/MS and Roche Elecsys Vitamin D total III achieved the optimal specification for bias (i.e., <3.4%). Imprecision, linearity and matrix effects showed acceptable results. The biotin interference threshold was increased up to 1,200 ng/mL and the outlier rate was low (0.26%). The cross-reactivity with 24,25(OH)₂D₃ and 3-epi-25(OH)D₃ was weak or modest in available patient samples. However, using SRM972a with a high level of 3-epi-25(OH)D₃ (enriched) revealed an important cross-reactivity with both Roche Elecsys Vitamin D total II and III assays (+74.7% and +73.7%).

In conclusion, the Roche Elecsys Vitamin D total III assay presents several advantages compared to the previous assay generation: higher biotin interference threshold, broader measuring range, and better comparability with LC-MS/MS. However, the cross-reactivity toward 3-epi-25(OH)D₃ is still problematic in high titer samples.