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Vitamin D

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Vitamin D

Does this test have other names?

25-hydroxyvitamin D (25-high-DROX-ee-VIE-tuh-min D), 25(OH)D

What is this test?

Vitamin D is mainly found in fortified dairy foods, juice, breakfast cereal, and certain fish. This vitamin plays many roles in the body. But because it helps the body absorb calcium from foods and supplements, it's particularly important for bone health. Vitamin D has many additional roles in the body.

Vitamin D comes in several forms. When ultraviolet light, such as sunlight, hits your skin, it creates vitamin D3. D2 is used to fortify dairy foods. Both of these are further processed by your liver and kidneys into a form your body can use. Most tests for vitamin D check the level of a form circulating in the body called 25-hydroxyvitamin D, also called 25(OH)D. 

Why do I need this test?

Vitamin D testing has become much more popular in recent years. Often, health care providers check vitamin D levels to investigate threats to bone health, such as low calcium; osteomalacia, or soft bones caused by low vitamin D or problems using it; osteopenia; osteoporosis; and rickets in children.

Vitamin D has many effects in the body, and testing may be needed while diagnosing or treating:

  • People with risk factors for low vitamin D, such as those of older age, who have difficulty absorbing fat from the diet or have chronic kidney disease, or who are dark skin pigmentation breastfed babies

  • Problems with the parathyroid gland

  • Cancer

  • Autoimmune diseases such as multiple sclerosis and Crohn's disease

  • Psoriasis

  • Asthma

  • Weakness or falls  

What other tests might I have along with this test?

A health care provider may also want to check your parathyroid hormone levels and your calcium levels. 

What do my test results mean?

A result for a lab test may be affected by many things, including the method the laboratory uses to do the test. If your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Children and adults need more than 30 nanograms per milliliter (ng/ml) of vitamin D. The optimal level of 25(OH)D is usually said to be 30 to 60 ng/mL. Recommended daily amounts range from 400 to 800 international units (IU) per day based on age.

Levels lower than normal can indicate that you're not producing enough vitamin D on your own, you're not consuming enough in your diet, you're not absorbing it properly from your food, or your body is not converting it properly, perhaps because of kidney or liver disease. Above-normal levels may be a sign that you're taking too much in supplement form. 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, and a sense of lightheadedness. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. 

What might affect my test results?

The amount of time you spend in the sunlight, your diet, and whether you take vitamin D in supplement form can affect your vitamin D levels.

How do I get ready for this test?

Tell the health care provider ordering your tests if you take vitamin D supplements, which could affect your results. Discuss whether any medical conditions you have or medications you're taking can affect your test results.