What is the role of serum 25(OH)D in the workup of vitamin D deficiency?

Updated: Dec 15, 2020
  • Author: Vin Tangpricha, MD, PhD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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This is the best test to determine vitamin D status (see Vitamin D3 25-Hydroxyvitamin D). The circulating half-life of 25(OH)D is 2 weeks. A 25(OH)D level of less than 30 ng/mL is considered vitamin D insufficient. [1] A 25(OH)D level of less than 15 or 20 ng/mL have been used to define vitamin D deficiency. Intestinal calcium absorption is optimized at levels above 30-32 ng/mL. [8, 39] Parathyroid hormone levels start to rise at 25(OH)D levels below 31 ng/mL, [69] which is another marker of vitamin D insufficiency. [70]

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