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.