The prevalence of vitamin deficiency in clinical practice is assay-dependent

Summary Background & aim Vitamin D deficiency is an important concern in clinical settings and recently, international agencies have recognised the importance of 25-OHD assays in defining vitamin D status. Thus, our aim was to assess the consistency of different vitamin D assays in clinical practice. Methods: 25-OH-vitamin D was measured in 332 patients by ultra-fast liquid chromatography (UHPLC) and two immunoassays (Liaison Total 25(OH) and ADVIA Centaur Vitamin D Total Assay). Samples from the Vitamin D External Quality Survey (DEQAS) and the Standard Reference Material SRM 972 were used for analytical quality control. Results: All methods displayed an acceptable performance with DEQAS samples but immunoassays showed a significant bias against certified materials. Compared to UHPLC, differences were significant for both immunoassays in the deficiency interval but the systematic bias was higher for the ADVIA assay throughout the whole range of concentrations. Conclusion: The prevalence of vitamin D deficiency in clinical practice is assay-dependent and physicians should be aware of the uncertainty associated with vitamin D assessment.