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25-hydroxy vitamin D test
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25-hydroxy vitamin D test

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25-OH vitamin D test; Calcidiol; 25-hydroxycholecalciferol test

The 25-hydroxy vitamin D test is the most accurate way to measure how much vitamin D is in your body.

In the kidney, 25-hydroxy vitamin D changes into an active form of the vitamin. The active form of vitamin D helps control calcium and phosphate levels in the body.

This article discusses the blood test used to measure the amount of 25-hydroxy vitamin D.

I Would Like to Learn About:

  • How the Test is Performed

    A blood sample is needed. For information on how this is done, see: Venipuncture

  • How to Prepare for the Test

    Usually you will not need to fast. However, this depends on the laboratory on the testing method used.

  • How the Test Will Feel

    When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

  • Why the Test is Performed

    This test is done to determine if you have too much or too little vitamin D in your blood.

  • Normal Results

    The normal range is 30.0 to 74.0 nanograms per milliliter (ng/mL).

    The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some laboratories use different measurements or test different samples.Talk to your doctor about the meaning of your specific test results.

  • What Abnormal Results Mean

    Lower-than-normal levels can be due to a vitamin D deficiency, which can result from:

    • Lack of exposure to sunlight
    • Lack of enough vitamin D in the diet
    • Liver and kidney diseases
    • Poor food absorption
    • Use of certain medicines, including phenytoin, phenobarbital, and rifampin

    Low vitamin D levels are more common in African-American children (especially in the winter), as well as in infants who are breastfed only. Low vitamin D levels have also been associated with an increased risk of developing cancer. For more information, see the article on vitamin D deficiency.

    Higher-than-normal levels may be due to excess vitamin D, a condition called hypervitaminosis D.

  • Risks

    Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

    Other risks associated with having blood drawn are slight but may include:

    • Excessive bleeding
    • Fainting or feeling light-headed
    • Hematoma (blood accumulating under the skin)
    • Infection (a slight risk any time the skin is broken)

Related Information

  Hyperparathyroidis...Hypervitaminosis D...Hypercalcemia    

References

Weng FL, Shults J, Leonard MB, Stallings VA, Zemel BS. Risk factors for low serum 25-hydroxyvitamin D concentrations in otherwise healthy children and adolescents. Am J Clin Nutr. 2007;86(1):150-158.

Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. Am J Clin Nutr. 2007;85(6):1586-1591.

Specker BL, Valanis B, Hertzberg V, Edwards N, Tsang RC. Sunshine exposure and serum 25-hydroxyvitamin D concentrations in exclusively breast-fed infants. J Pediatr 1985;107(3):372-376.

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Review Date: 7/19/2012  

Reviewed By: Shehzad Topiwala, MD, Chief Consultant Endocrinologist, Premier Medical Associates, The Villages, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.

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