To determine if you have a vitamin D deficiency; if you are receiving vitamin D supplementation, to determine if it is adequate
Vitamin D Tests
Vitamin D Tests
Also Known As
Ergocalciferol (Vitamin D2)
Cholecalciferol (Vitamin D3)
Calcidiol (25-hydroxyvitamin D)
Calcifidiol (25-hydroxy-vitamin D)
Calcitriol (1,25 dihydroxy-vitamin D)
Formal Name
25-hydroxyvitamin D
1,25 dihydroxyvitamin D
This article was last reviewed
on
This article waslast modified
on March 24, 2021.
At a Glance
Why Get Tested?
When To Get Tested?
When you have an abnormal calcium, phosphorus, and/or parathyroid hormone level; when you have evidence of bone disease or bone weakness; when you are at high risk of deficiency or a healthcare practitioner suspects that you might have a vitamin D deficiency; prior to starting drug treatment for osteoporosis; periodically to monitor treatment of vitamin D deficiency
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None
Accordion Title
Common Questions
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How is it used?
A vitamin D test is used to:
- Determine if bone weakness, bone malformation, or abnormal metabolism of calcium (reflected by abnormal calcium, phosphorus, PTH) is occurring as a result of a deficiency or excess of vitamin D
- Help diagnose or monitor problems with parathyroid gland functioning since PTH is essential for vitamin D activation
- Screen people who are at high risk of deficiency, as recommended by the National Osteoporosis Foundation, the Institute of Medicine, and the Endocrine Society
- Help monitor the health status of individuals with diseases that interfere with fat absorption, such as cystic fibrosis and Crohn disease, since vitamin D is a fat-soluble vitamin and is absorbed from the intestine like a fat
- Monitor people who have had gastric bypass surgery and may not be able to absorb enough vitamin D
- Help determine the effectiveness of treatment when vitamin D, calcium, phosphorus, and/or magnesium supplementation is prescribed
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When is it ordered?
25-hydroxyvitamin D
When calcium is low and/or a person has symptoms of vitamin D deficiency, such as bone malformation in children (rickets) and bone weakness, softness, or fracture in adults (osteomalacia), 25-hydroxyvitamin D usually is ordered to identify a possible deficiency in vitamin D.The test may be requested when an individual is known to be at risk of vitamin D deficiency. Older adults, people who are institutionalized or homebound and/or have limited sun exposure, those who are obese, who have undergone gastric bypass surgery, and/or who have fat malabsorption are at an increased risk of a vitamin D deficiency. Also included in this group are people with darker skin and breastfed infants.
25-hydroxyvitamin D is often requested before an individual begins drug therapy for osteoporosis.
1,25-dihydroxyvitamin D
This testing may be ordered when kidney disease or abnormalities of the enzyme that converts 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D is suspected. Rarely, this test may be done when calcium is high or a person has a disease that might produce excess amounts of vitamin D, such as sarcoidosis or some forms of lymphoma (because immune cells may make 1,25-dihydroxyvitamin D).When vitamin D, calcium, phosphorus, or magnesium supplementation is necessary, vitamin D levels are sometimes measured to monitor treatment effectiveness.
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What does the test result mean?
Although there are differences among vitamin D methods, most laboratories utilize similar reference intervals. Because toxicity is rare, the focus has been on the lower limit and what cut-off for total 25-hydroxyvitamin D (D2 + D3) indicates deficiency.
- The Endocrine Society defines vitamin D deficiency as a 25-hydroxyvitamin D blood level below 20 ng/mL (50 nmol/liter) and vitamin D insufficiency as a level between 21–29 ng/mL (52.5–72.5 nmol/liter).
- The U.S. Institute of Medicine has concluded that a 25-hydroxyvitamin D level of 20 ng/mL (50 nmol/liter) or above is adequate for bone health, and that levels greater than 30 ng/mL do not offer significantly better effects. However, it is fair to say that the level of 25-hydroxyvitamin D associated with protection from the many other disorders recently associated with a lack of vitamin D is controversial.
25-hydroxyvitamin D
A low blood level of 25-hydroxyvitamin D may mean that a person is not getting enough exposure to sunlight or enough dietary vitamin D to meet his or her body's demand or that there is a problem with its absorption from the intestines. Occasionally, drugs used to treat seizures, particularly phenytoin (Dilantin), can interfere with the production of 25-hydroxyvitamin D in the liver.There is some evidence that vitamin D deficiency may increase the risk of some cancers, immune diseases, and cardiovascular disease.
A high level of 25-hydroxyvitamin D usually reflects excess supplementation from vitamin pills or other nutritional supplements.
1,25-dihydroxyvitamin D
A low level of 1,25-dihydroxyvitamin D can be seen in kidney disease and is one of the earliest changes to occur in persons with early kidney failure.A high level of 1,25-dihydroxyvitamin D may occur when there is excess parathryoid hormone or when there are diseases, such as sarcoidosis or some lymphomas, that can make 1,25-dihydroxyvitamin D outside of the kidneys.
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Is there anything else I should know?
High levels of vitamin D and calcium can lead to the calcification and damage to organs, particularly the kidneys and blood vessels.
If magnesium levels are low, they can cause a low calcium level that is resistant to vitamin D and parathyroid hormone regulation. It may be necessary to supplement both magnesium and calcium to regain normal function.
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How much vitamin D should I be getting each day?
It depends on your age and sex. In 2010, the Institute of Medicine set the Dietary Reference Intake (DRI) for both calcium and vitamin D. For details, see the report: DRIs for Calcium and Vitamin D.
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Is fortifying milk and cereals with vitamin D a good practice?
Yes. The amount of vitamin D produced by the body may be insufficient, especially when there is limited exposure to sunlight and routine use of sunscreens. Since dietary vitamin D is found naturally only in a few foods, such as cod liver oil, dietary intake would not be sufficient for most people. However, in the United States, vitamin D is routinely added to milk, fortified cereals, and fruit juices to ensure adequate dietary availability. Fortification of milk and infant formula has been a real success story in the United States, drastically reducing the rate of juvenile rickets and making it a relatively rare occurrence.
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Can I get my vitamin D from yogurt and cheese?
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Are there other uses for vitamin D?
Yes, there is a topical form of vitamin D cream that is used to treat psoriasis. Research is being done in other areas, including the potential use of vitamin D to help control autoimmune conditions.
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Is vitamin D a necessary component of calcium supplements?
Since absorption of calcium is dependent on vitamin D, many manufacturers of calcium supplements add vitamin D to assure optimal calcium uptake. If you have adequate amounts of vitamin D from other sources, the additional vitamin D is not necessary. The amount of vitamin D in these tablets is not likely to lead to excess vitamin D or be harmful either.
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