Evaluation of the new restandardized Abbott Architect 25-OH Vitamin D assay in vitamin D-insufficient and vitamin D-supplemented individuals

Background: Recently, Abbott Diagnostics has restandardized the Architect 25(OH) D assay against the NIST SRM 2972. We have evaluated the analytical and clinical performance of the restandardized Architect 25(OH) D assay and compared its performance with a NIST-traceable liquid chromatography-tandem mass spectrometry (LC-MS/MS) method and the Roche total 25(OH) D assay in vitamin D-insufficient individuals before and after vitamin D-3 supplementation. Methods: Frozen serum samples were obtained from 88 healthy subjects with self-perceived fatigue and vitamin D-insufficiency < 50 nmol L-1 who were randomized to receive a single 100 000 IU dose of vitamin D-3 (n = 48) or placebo (n = 40). Total 25(OH) D concentrations were measured before and 4 weeks after supplementation by the restandardized Architect 25(OH) D assay, LC-MS/MS, and Roche assay. Results: The Architect 25(OH) D assay showed an intra-and inter-assay imprecision of < 5%. Comparison of the Architect assay with the LC-MS/MS method showed a good correlation in both vitamin D-insufficient and vitamin D-supplemented subjects, however, with a negative mean bias of 17.4% and 8.9%, respectively. As compared to the Roche assay, the Abbott assay underestimated 25(OH) D results in insufficient subjects (< 50 nmol L-1) with a mean negative bias of 17.1%, this negative bias turned into a positive bias in supplemented subjects. Overall there was a moderate agreement in classification of vitamin D-insufficient and -supplemented individuals into different vitamin D states between the Architect 25(OH) D method and LC-MS/MS. Conclusion: The routine use of the restandardized Architect 25(OH) D results in a slight underestimation of circulating total 25(OH) D levels at lower concentrations and thus potential misclassification of vitamin D status.