What is a vitamin D test?
Vitamin D is a nutrient that is essential for healthy bones and teeth. There are two forms of vitamin D that are important for nutrition: vitamin D2 and vitamin D3. Vitamin D2 mainly comes from fortified foods like breakfast cereals, milk, and other dairy items. Vitamin D3 is made by your own body when you are exposed to sunlight. It is also found in some foods, including eggs and fatty fish, such as salmon, tuna, and mackerel.
In your bloodstream, vitamin D2 and vitamin D3 are changed into a form of vitamin D called 25 hydroxyvitamin D, also known as 25(OH)D. A vitamin D blood test measures the level of 25(OH)D in your blood. Abnormal levels of vitamin D can indicate bone disorders, nutrition problems, organ damage, or other medical conditions.
Other names: 25-hydroxyvitamin D, 25(OH)D
What is it used for?
A vitamin D test is used to screen for or monitor bone disorders. It is also sometimes used to check vitamin D levels in people with chronic illnesses such as asthma, psoriasis, and certain autoimmune diseases.
Why do I need a vitamin D test?
Your health care provider may have ordered a vitamin D test if you have symptoms of a vitamin D deficiency (not enough vitamin D). These symptoms include:
- Bone weakness
- Bone softness
- Bone malformation (in children)
The test may be ordered if you are at a higher risk for a vitamin D deficiency. Risk factors include:
- Osteoporosis or other bone disorder
- Previous gastric bypass surgery
- Age; vitamin D deficiency is more common in older adults.
- Lack of exposure to sunlight
- Having a darker complexion
- Difficulty absorbing fat in your diet
In addition, breastfed babies may be at a higher risk if they aren’t taking vitamin D supplements.
What happens during a vitamin D test?
A vitamin D test is a blood test. During a blood test, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Will I need to do anything to prepare for the test?
You don’t need any special preparations for a vitamin D test.
Are there any risks to the test?
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
What do the results mean?
If your results show a deficiency in vitamin D, it may mean you are:
- Not getting enough exposure to sunlight
- Not getting enough vitamin D in your diet
- Having trouble absorbing vitamin D in your food
A low result may also mean your body is having trouble using the vitamin as it should, and may indicate kidney or liver disease.
A vitamin D deficiency is usually treated with supplements and/or dietary changes.
If your results show you have an excess of (too much) vitamin D, it is most likely due to taking too many vitamin pills or other supplements. You’ll need to stop taking these supplements to reduce your vitamin D levels. Too much vitamin D can cause damage to your organs and blood vessels.
To learn what your results mean, talk to your health care provider.
Is there anything else I need to know about a vitamin D test?
Be sure to tell your health care provider about medicines, vitamins, or supplements you are taking, because they can affect your test results.
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- National Institutes of Health: Office of Dietary Supplements [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Vitamin D: Fact Sheet for Health Professionals [updated 2016 Feb 11; cited 2017 Apr 10]; [about 3 screens]. Available from: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#h10
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