External Quality Assessment of 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) assays. 2019

G D Carter, and F Ahmed, and J Berry, and E Cavalier, and R Durazo-Arvizu, and E Gunter, and G Jones, and J Jones, and K Phinney, and C T Sempos, and P J Twomey, and E L Williams, and S A Wise
Imperial College Healthcare NHS Trust, Charing Cross Hospital, London, W6 8RF, United Kingdom. Electronic address: grahamdcarter130@gmail.com.

The discovery that mutations of the CYP24A1 gene are a cause of idiopathic infantile hypercalcemia (IIH) has revived interest in measuring serum 24,25(OH)2D3. Several studies have also suggested that a high 25-hydroxyvitamin D3(25-OHD3):24,25(OH)2D3 ratio might provide additional diagnostic information in the investigation of vitamin D deficiency. Measurement of 24,25(OH)2D3 is necessarily restricted to laboratories with mass spectrometry methods although cross reactivity of the metabolite in immunoassays for 25-OHD is a potential cause of misleading results. The international External Quality Assessment (EQA) scheme for vitamin D metabolites (DEQAS) was set up in 1989. In 2013 DEQAS became an accuracy based EQA for 25-OHD with 'target values' assigned by the National Institute of Standards and Technology (NIST) Reference Measurement Procedure (RMP). A pilot scheme for serum 24,25(OH)2D3 was started in 2015 and participants were asked to measure the metabolite on each of the 5 samples sent out for 25-OHD. Inter-laboratory agreement was poor but this may reflect methodological differences, in particular different approaches to assay standardization. An important potential contribution to reducing variability among assays was the development by NIST of a 24,25(OH)2D3 RMP and its use in assigning values to SRMs 972a, 2973 and 2971, supported by the NIH Office of Dietary Supplements (ODS) as part of the Vitamin D Standardization Program (VDSP) effort.

UI MeSH Term Description Entries
D011786 Quality Control A system for verifying and maintaining a desired level of quality in a product or process by careful planning, use of proper equipment, continued inspection, and corrective action as required. (Random House Unabridged Dictionary, 2d ed) Control, Quality,Controls, Quality,Quality Controls
D012015 Reference Standards A basis of value established for the measure of quantity, weight, extent or quality, e.g. weight standards, standard solutions, methods, techniques, and procedures used in diagnosis and therapy. Standard Preparations,Standards, Reference,Preparations, Standard,Standardization,Standards,Preparation, Standard,Reference Standard,Standard Preparation,Standard, Reference
D002853 Chromatography, Liquid Chromatographic techniques in which the mobile phase is a liquid. Liquid Chromatography
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D014807 Vitamin D A vitamin that includes both CHOLECALCIFEROLS and ERGOCALCIFEROLS, which have the common effect of preventing or curing RICKETS in animals. It can also be viewed as a hormone since it can be formed in SKIN by action of ULTRAVIOLET RAYS upon the precursors, 7-dehydrocholesterol and ERGOSTEROL, and acts on VITAMIN D RECEPTORS to regulate CALCIUM in opposition to PARATHYROID HORMONE.
D014815 Vitamins Organic substances that are required in small amounts for maintenance and growth, but which cannot be manufactured by the human body. Vitamin
D053719 Tandem Mass Spectrometry A mass spectrometry technique using two (MS/MS) or more mass analyzers. With two in tandem, the precursor ions are mass-selected by a first mass analyzer, and focused into a collision region where they are then fragmented into product ions which are then characterized by a second mass analyzer. A variety of techniques are used to separate the compounds, ionize them, and introduce them to the first mass analyzer. For example, for in GC-MS/MS, GAS CHROMATOGRAPHY-MASS SPECTROMETRY is involved in separating relatively small compounds by GAS CHROMATOGRAPHY prior to injecting them into an ionization chamber for the mass selection. Mass Spectrometry-Mass Spectrometry,Mass Spectrometry Mass Spectrometry,Mass Spectrometry, Tandem

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