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?

You may need this test if your healthcare provider wants to 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 healthcare provider diagnose or treat:

• Problems with the parathyroid gland

• Cancer

• Autoimmune diseases, such as multiple sclerosis and inflammatory bowel 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?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

Although exact levels have not been identified, experts believe that levels of 20 nanograms per milliliter (ng/mL) or higher are enough for good bone and overall health. 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 is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.

What might affect my test results?

Your age, 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. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.