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25-hydroxy vitamin D test

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Vitamins

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Hypercalcemia Hyperparathyroidism Hypervitaminosis D

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.

How the Test is Performed

Blood is typically drawn from a vein, usually from the inside of the
elbow or the back of the hand. The site is cleaned with germ-killing
medicine (antiseptic). The health care provider wraps an elastic band
around the upper arm to apply pressure to the area and make the vein
swell with blood.

Next, the health care provider gently inserts a needle into the vein.
The blood collects into an airtight vial or tube attached to the
needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the
puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used
to puncture the skin and make it bleed. The blood collects into a
small glass tube called a pipette, or onto a slide or test strip. A
bandage may be placed over the area if there is any bleeding.

How to Prepare for the Test

Do not eat for 4 hours before the test.

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).

Note: Normal value ranges may vary slightly among different
laboratories. Talk to your doctor about the meaning of your specific
test results.

What Abnormal Results Mean

Lower-than-normal levels suggest a vitamin D deficiency. This
condition can result from:

Lack of exposure to sunlight

Lack of adequate vitamin D in the diet

Liver and kidney diseases

Malabsorption

Use of certain medicines, including phenytoin, phenobarbital, and
 rifampin

Low vitamin D levels are more common in African-American children,
particularly in the winter, as well as in infants who are exclusively
breastfed. 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 suggest 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)

Alternative Names

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

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):372-6.

Update Date: 7/28/2008

Updated by: Robert Cooper, MD, Endocinology Specialist and Chief of
Medicine, Holyoke Medical Center, Assistant Professor of Medicine,
Tufts University School of Medicine, Boston MA Review provided by
VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA,
Medical Director, A.D.A.M., Inc.

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