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|Section2= |Section6= |Section7= }} Calcifediol (INN), also known as calcidiol, 25-hydroxycholecalciferol, or 25-hydroxyvitamin D (abbreviated 25(OH)D),〔("Nomenclature of Vitamin D. Recommendations 1981. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN) )" reproduced at the Queen Mary, University of London website. Retrieved 21 March 2010.〕 is a prehormone that is produced in the liver by hydroxylation of vitamin D3 (cholecalciferol) by the enzyme cholecalciferol 25-hydroxylase which was isolated by Michael F. Holick. Physicians worldwide measure this metabolite to determine a patient's vitamin D status. At a typical daily intake of vitamin D3, its full conversion to calcifediol takes approximately 7 days.〔Am J Clin Nutr 2008;87:1738–42 PMID 18541563〕 Calcifediol is then converted in the kidneys (by the enzyme 25(OH)D-1α-hydroxylase) into calcitriol (1,25-(OH)2D3), a secosteroid hormone that is the active form of vitamin D. It can also be converted into 24-hydroxycalcidiol in the kidneys via 24-hydroxylation.〔 Retrieved December 10, 2008 through Google Book Search.〕 ==Blood test== In medicine, a 25-hydroxy vitamin D (calcidiol) blood test is used to determine how much vitamin D is in the body.〔("25-hydroxy vitamin D test: Medline Plus" ). Retrieved 21 March 2010.〕 The blood concentration of calcidiol is considered the best indicator of vitamin D status. This test can be used to diagnose vitamin D deficiency, and it is indicated in patients with high risk for vitamin D deficiency and when the results of the test would be used as supporting evidence for beginning aggressive therapies.〔, which cites # * # * # *, which cites # * * # *〕 Patients with osteoporosis, chronic kidney disease, malabsorption, obesity, and some other infections may be high risk and thus have greater indication for this test.〔 Although vitamin D deficiency is common in some populations including those living at higher latitudes or with limited sun exposure, the 25(OH)D test is not indicated for entire populations.〔 Physicians may advise low risk patients to take over-the-counter vitamin D in place of having screening.〔 It is the most sensitive measure,〔Institute of Medicine (1997), p. 259〕 though experts have called for improved standardization and reproducibility across different laboratories.〔 According to MedlinePlus, the normal range of calcidiol is 30.0 to 74.0 ng/mL.〔 The normal range varies widely depending on several factors, including age and geographic location. A broad reference range of 20–150 nmol/L (8-60 ng/ml) has also been suggested,〔 Retrieved December 10, 2008 through Google Book Search.〕 while other studies have defined levels below 80 nmol/L (32 ng/ml) as indicative of vitamin D deficiency. US labs generally report 25(OH)D levels as ng/mL. Other countries often use nmol/L. Multiply ng/mL by 2.5 to convert to nmol/L. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Calcifediol」の詳細全文を読む スポンサード リンク
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