Current 25-hydroxyvitamin D assays: Do they pass the test?

Abstract

BackgroundVitamin D testing is becoming increasingly important with recent research demonstrating a correlation between vitamin D insufficiency and metabolic diseases, immunodeficiencies and other diseases. However, existing 25-hydroxyvitamin D (25OHD) assays lack comparability to the candidate reference method, causing difficulties in diagnosis and monitoring of vitamin D deficiency. MethodsWe looked at the accuracy of 3 automated assays (Roche Diagnostics Elecsys® Total 25OHD assay, Abbott Architect® Total vitamin D assay, Advia Centaur® vitamin D Total assay) and Diasorin® Radioimmunoassay (RIA) compared to a routine laboratory Liquid Chromatography–Tandem Mass Spectrometry (LC–MS/MS). ResultsThe correlation based on Passing Bablok regression was good with the slopes between 0.95 and 1.31 and the intercepts between −3.24 and 3.68. However, a significant positive bias was observed using the Abbott Architect and the Diasorin RIA. Using published analytical goals of coefficient of variation (CV) <10% and bias <5%, most methods did not meet these criteria. Using measurement of uncertainty of 9%, most methods were able to meet criteria using quality control materials but not patient samples. ConclusionInadequacies of these assay performances are contributed by differences in method of extraction of vitamin D from vitamin D binding protein, cross-reactivities to 25OHD2, 25OHD3 and other vitamin D metabolites, matrix interferences and a lack of standardization.