title: Interpreting vitamin D assay results: proceed with caution.
abstract: Vitamin D deficiency and insufficiency are common in patients with CKD. Association studies suggest that low 25-hydroxyvitamin D3 (25-OH-D3) is a harbinger of poor outcomes in these patients. Serum 25-OH-D represents the best biomarker of vitamin D status, but there is much debate surrounding the performance of some of the assay methods. Programs such as the Vitamin D Standardization Program and Vitamin D External Quality Assessment Scheme (DEQAS) in the United Kingdom have allowed us to assess the accuracy and reproducibility of the available methods. Liquid chromatography-tandem mass spectrometry-based methods for serum 25-OH-D measurement are emerging as more accurate and reliable alternatives to the immunoassay-based methods that have dominated over the past 2 decades. There is a renewed optimism that serum 25-OH-D is a useful biomarker to be used in patients with CKD, in particular to diagnose vitamin D deficiency and monitor vitamin D therapy. This commentary discusses some of the methodologic problems associated with serum 25-OH-D assays and their resolution, and looks forward to the future of vitamin D testing.
authors.affiliation: Department of Biomedical & Molecular Sciences, Queen's University, Kingston, Ontario Canada gj1@queensu.ca.
authors.forename: Glenville
authors.initials: G
authors.lastname: Jones
mesh_terms: D015415:Biomarkers / Q000097:blood; D002112:Calcifediol / Q000097:blood*; D002853:Chromatography, Liquid / Q000592:standards; D006801:Humans; D007118:Immunoassay / Q000592:standards; D015588:Observer Variation; D011237:Predictive Value of Tests; D011379:Prognosis; D019984:Quality Indicators, Health Care; D051436:Renal Insufficiency, Chronic / Q000453:epidemiology; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry / Q000592:standards; D013997:Time Factors; D006113:United Kingdom; D014808:Vitamin D Deficiency / Q000097:blood / Q000175:diagnosis* / Q000188:drug therapy / Q000453:epidemiology
chemical_list: D015415:Biomarkers; D002112:Calcifediol
keywords: Vitamin D; calcium; chronic kidney disease; dialysis; hyperparathyroidism
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