A Comparison between Three Different Automated Total 25-hydroxyvitamin D Immunoassay Methods and Ultra Performance Liquid Chromatography

OBJECTIVE: Vitamin D is a fat soluble vitamin responsible for calcium metabolism and more recently discovered effects. This led to an increase in requests for vitamin D test by clinicians. New automated assays have been introduced for 25-hydroxyvitamin D measurement. METHODS: Results from these new method have to be related to a Standard method to obtain best results for practical usage. In our study, one hundred venous blood samples were analyzed for 25-OH vitamin D on three immunological methods in our lab and correlated with ultra-performance liquid chromatography (UPLC) method as a reference method. RESULTS: Statistically analysis of results obtained for correlations between the 3 methods against the reference UPLC was done by Spearman’s Correlation. It showed positive correlation in all methods with significant p value < 0.001. Differences and biases between methods were evaluated using a Bland-Altman plot and Cohen’s Kappa agreement. Best agreement was found in Cobas 6000 followed by the Access2 then comes Architect. CONCLUSIONS: All immunoassays can be used in routine 25(OH) D measurements, still some methods are better than others. A clinical laboratory must at least be aware of its method to avoid misinterpretation of results.