Lack of transferability between different immunoassays and LC-MS/MS for total 25-hydroxyvitamin D measurement and disagreement defining deficiency

Abstract

Background. Over the last few years, it has become much more common to measure concentrations of vitamin D, as its deficiency has been associated with an increasing number of health problems. Recently, a number of new immunoassays for measurement of total 25-hydroxyvitamin D (25OH-D) concentration have been released but their results may not be transferable. Methods. Our main objective was to compare results from the Cobas^® e411 (Roche Diagnostics), Advia Centaur^® (Siemens), Architect (Abbott), IDS-iSYS (Vitro S.A.), and Liaison^® (Diasorin) immunoassay systems with each other and with liquid chromatography-tandem mass spectrometry (LC-MS/MS). We obtained 184 routine serum samples, covering the whole measuring range, for these methods. Results. Kappa values above 0.8 were considered to indicate excellent agreement. With a cut-off of 50 nmol/L Architect and Cobas were the only immunoassay methods able to identify patients with deficiencies consistent with the findings of the reference method LC-MS/MS. On the other hand, using a cut-off of 37.5 nmol/L for Liaison and 75 nmol/L for IDS-iSYS, while maintaining the value of 50 nmol/L for the LC-MS/MS method, kappa values of 0.80 and 0.83 respectively were obtained. Conclusions. Choosing the best method for each laboratory is challenging due to methodological differences between them and 50 nmol/L cannot be considered as a general cut-off for defining hypovitaminosis.

Key Words::

• Deficiency
• immunoassay
• methods
• reference levels
• serum
• vitamin D

Acknowledgements

We are grateful to Roche Diagnostics, Siemens Healthcare Diagnostics, Abbott Diagnostics, Vitro and Diasorin for providing the 25OH-D reagents free of charge.

Author contributions: All authors confirm that they have contributed to the intellectual content of this paper and have met the following three requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.