Vitamin D Blood Test

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Latest Edit: Hector 2014-03-21 (EDT)

See Also Lab Tests

This test is conducted to determine vitamin D deficiency, to determine if vitamin D supplementation level is appropriate, or if a person is receiving vitamin D therapy.[1], [2]


  • Two forms of vitamin D can be measured in the blood; 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1, 25(OH)(2)D].
  • 25-hydroxyvitamin D is the major form of the hormone found in the blood and is the inactive precursor to the active hormone, 1,25-dihydroxyvitamin D.
  • The sources of vitamin D include endogenous sources, produced in the skin on exposure to sunlight, and exogenous sources such as foods and supplements.
  • The main role of vitamin D is to help regulate the absorption of calcium, phosphorus, and magnesium (to a lesser extent).
  • Since vitamin D is a fat-soluble vitamin and is absorbed from the intestine like a fat, it is sometimes used to monitor individuals with diseases that interfere with fat absorption, such as cystic fibrosis and Crohn's disease.

Patient Preparation

  • No preparation is required.

Clinical Implications

High levels indicate:

  • Excess supplementation (pills or other nutritional supplements)
  • Sarcoidosis
  • Lymphomas

Low levels indicate:

Associated Tests


  1. Pagana Kathleen D, Pagana Timothy J (2006) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby.
  2. Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain.