Performance characteristics of the VIDAS® 25-OH Vitamin D Total assay - comparison with four immunoassays and two liquid chromatography-tandem mass spectrometry methods in a multicentric study.

Background: The study was conducted to evaluate the analytical and clinical performance of the VIDAS® 25-OH Vitamin D Total assay. The clinical performance of the assay was compared with four other immunoassays against the results of two different liquid chromatography/mass spectrometry methods (LC-MS/MS) standardized to NIST reference materials.

Methods: VIDAS® 25-OH Vitamin D Total assay precision, linearity, detection limits and sample matrix comparison were assessed following CLSI guidelines. For method comparison, a total of 150 serum samples ranging from 7 to 92 ng/mL were analyzed by all the methods. Correlation was studied using Passing-Bablok regression and Bland-Altman analysis. The concordance correlation coefficient (CCC) was calculated to evaluate agreement between immunoassays and the reference LC-MS/MS method. In addition, samples containing endogenous 25(OH)D2 were used to assess each immunoassay's ability to detect this analyte. Pregnancy and hemodialysis samples were used to the study the effect of vitamin D binding protein (DBP) concentration over VIDAS® assay performance.

Results: The VIDAS® 25-OH Vitamin D Total assay showed excellent correlation to the LC-MS/MS results (y=1.01x+0.22 ng/mL, r=0.93), as obtained from two different sites and distinct LC-MS/MS methods. The limit of quantification was determined at 8.1 ng/mL. Cross-reactivity for 25(OH)D2 was over 80%. At concentrations of 10.5, 26 and 65.1 ng/mL, within-run CVs were 7.9%, 3.6% and 1.7%, while total CVs (between runs, calibrations, lots and instruments) were 16.0%, 4.5% and 2.8%. The VIDAS® performance was not influenced by altered DBP levels, though under-recovery of 25(OH)D as compared to LC-MS/MS was observed for hemodialysis samples.

Conclusions: The VIDAS® 25-OH Vitamin D Total assay is therefore considered suitable for assessment of vitamin D status in clinical routine.