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RESEARCH PRODUCT

Standardized measurement of circulating vitamin D [25(OH)D] and its putative role as a serum biomarker in Alzheimer's disease and Parkinson's disease

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The current review provides an overview on the development of 25(OH)D measurement standardization tools over the last three decades and clarifies whether there is a role as a serum biomarker for vitamin D in neurological diseases. In the past, a lack of internationally recognized 25(OH)D reference measurement procedures and reference standard materials led to unstandardized serum total 25(OH)D results among research and clinical care laboratories. The vitamin D Standardization Program (VDSP) has been introduced in 2010 to address this problem, however, vitamin D External Quality Assessment Scheme (DEQAS) reports still show substantial sample- to- sample variability. Further, immunoassays, which are mainly used in clinical care laboratories, display analytical issues, including matrix-effects interferences, which cannot be overcome by the standardization process. Hence, liquid chromatography-tandem mass spectrometry (LC/MS-MS) methods should be used to measure 25(OH)D. Low vitamin D serum levels have been found in patients affected by Alzheimer's disease and Parkinson's disease, suggesting a role for vitamin D as a serum biomarker in these diseases. However, few studies reported 25(OH)D standardized results, thus, no clear evidence on the potential role of 25(OH)D serum levels in these diseases exists.