Comparison of automated methods for measurement of 25-hydroxyvitamin D

The objective of the study was to compare the analytical performance of three automated immunoassays for the determination of serum 25-hydroxyvitamin D.

Quantitative determination of serum 25(OH)D were performed by "Vitamin D total" (n = 131) and "Vitamin D3(25-OH)" (n = 77) assays (Roche Diagnostics) on a Cobas e411 and by "25-OH Vitamin D" (n = 131) assay (Abbott Laboratories) on an Architect. The inter-assay precision was calculated and methods were compared by the Passing Bablok regression and Bland-Altman analysis.

The "Vitamin D total" demonstrated stronger correlation (r = 0.863) and better agreement (bias = -7.89 nmol/L) with the "25-OH Vitamin D" than with the "Vitamin D3(25-OH)" (r = 0.716; bias = +18.6 nmol/L). The inter-assay precision (% CV) for the "Vitamin D total" and "25-OH Vitamin D" assays, were respectively 3.47 to 6.14 and 4.27 to 8.56.

The results of this study demonstrate that Abbott "25-OH Vitamin D" and Roche "Vitamin D total" are rapid and precise methods for 25(OH)D serum measurement over a wide reportable range on automated immunoassay platforms. The Abbott assay exhibited better correlation and agreement with the new Roche assay than the "Vitamin D3(25-OH)" Roche assay. Between method differences observed in this study still indicates the need for standardization of 25(OH)D assays.