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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. Your healthcare provider may check your vitamin D levels to find out if you have any risks to bone health. These might be:

  • Low calcium

  • Soft bones caused by low vitamin D or problems using it (osteomalacia)

  • Osteopenia

  • Osteoporosis

  • Rickets, in children

You may also need this test if you are at risk for low vitamin D levels. Risks include:

  • Being an older adult

  • Having difficulty absorbing fat from your diet

  • Having chronic kidney disease

  • Have dark skin pigmentation

  • Being a breastfed baby

Vitamin D has many effects in the body. You may need this test to help your provider diagnose or treat:

  • 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 healthcare 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 healthcare 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 between 30 and 60 ng/mL. Recommended daily amounts range from 400 to 800 international units (IU) per day based on your age.

Levels lower than normal can mean you are:

  • Not making enough vitamin D on your own

  • Not getting enough vitamin D in your diet

  • Not absorbing vitamin D from your food as you should

Lower levels may also mean that your body is not converting the vitamin as it should. This might be 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. Ask your healthcare provider if any health conditions you have or medicines you take could affect your results.

How do I get ready for this test?

Tell your healthcare provider if you take vitamin D supplements. Also be sure your provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use. 

Online Medical Reviewer: Snyder, Mandy, APRN
Online Medical Reviewer: Taylor, Wanda L, RN, PhD
Date Last Reviewed: 10/12/2015
© 2000-2017 The StayWell Company, LLC. 800 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.