25-Hydroxy Vitamin D Test

Written by Eric Searleman | Published on July 25, 2012
Medically Reviewed by George Krucik, MD


Vitamin D helps your body absorb calcium and maintain strong bones throughout your entire life. Vitamin D2 and D3 come from the fish, eggs, and fortified dairy products you eat. Cholesterol in your blood is converted by sunlight to provide additional D3.

Both D2 and D3 are important for proper body function.

The 25-hydroxy vitamin D test is the best way to monitor vitamin D levels. The test can determine if your body has a deficiency or excess of vitamin D. It serves as an important indicator of osteoporosis (bone weakness), rickets (bone malformation), and an unusual metabolism of calcium.

The test is also referred to as the 25-OH vitamin D test and the calcidiol 25-hydroxycholecalcifoerol test.

How Is the 25-hydroxy Vitamin D Test Performed?

The 25-hydroxy vitamin D test requires a common blood test. A healthcare provider will draw blood from a vein in your arm using a needle. A quick finger prick will more than likely provide an adequate blood sample for children and infants.

(Keep in mind that you will have to abstain from eating for about four to eight hours before the test.)

Evaluating the Results of a 25-hydroxy Vitamin D Test

No certain number range indicates vitamin D deficiency. Instead, results depend on the patient’s age, gender, and the testing methods used. Results can vary slightly from lab to lab.

Low blood levels of 25-hydroxy vitamin D usually mean that:

  • you aren’t eating right
  • your intestines aren’t absorbing the vitamin properly
  • you’re not spending enough time outside to absorb adequate vitamin D levels through sun exposure

There is evidence that a vitamin D deficiency points to a higher risk of certain cancers, immune diseases, and cardiovascular disease.

Low levels of vitamin D are common in African-American children. Infants who are exclusively breastfed are more likely to be deficient in vitamin D than those who aren’t.

High vitamin D blood levels generally result from ingesting too many vitamin pills and other nutritional supplements. Taking high doses of vitamin D can result in a condition called hypervitaminosis D. Hypervitaminosis is a rare, but serious condition that could put you at risk for liver or kidney problems.

High levels are rarely due to consuming too much of the vitamin through foods or sun exposure.

Your doctor will help explain the results of your test and determine if you are truly suffering from a vitamin D deficiency.

Risks of a 25-hydroxy Vitamin D Test

Risks involved with the 25-hydroxy vitamin test are the same as those for any routine blood test. Slight risks include: excessive bleeding, lightheadedness, and a slight chance of infection where the needle pierces your skin.

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