We evaluated three commercially available vitamin D assays to evaluate and compare the correlation and accuracy among them.Methods
Vitamin D was measured in 71 patient samples using the Architect 25-OH vitamin D assay (Abbott), the ADVIA Centaur vitamin D total assay (Siemens), and the LIAISON 25 OH vitamin D total assay (Diasorin). The evaluation made use of both patient samples and standard reference material, SRM 972. To analyze correlations and differences, Pearson's correlation coefficients and paired sample t-tests were performed.Results
Correlations among the three evaluated assays showed strong positive linear relationships (correlations among Siemens and DiaSorin, DiaSorin and Abbott, Abbott and Siemens: r=0.935, r=0.927, r=0.909, respectively). Mean (SD) vitamin D values on Siemens, Abbott, and DiaSorin assays in the 71 patient samples were 23.09 (10.41), 16.75 (11.26), and 16.76 (9.32), respectively. Results for the Siemens assay were significantly different from the other two methods (P<0.001). Target values for SRM 972 level 1, 2, 3, and 4 were 23.9, 14.0, 44.9, and 35.4, respectively. The Abbott, Siemens, and Diasorin assay values were closest to the target values in level 1, levels 2 and 3, and level 4, respectively.Conclusions
Correlations among vitamin D assays were good; however, the mean values of the Siemens assay were significantly higher than those of DiaSorin or Abbott. We found significant differences in vitamin D levels and discrepancies between patient samples and SRM 972 samples, which should be considered during use in a clinical setting.