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Vitamin D (25-Hydroxy)

Also known as Calcidiol, 25-hydroxycholecalciferol , Vit D (25-OH)

You need to provide

Blood

This test is for

Male, Female

Understanding Vitamin D (25-Hydroxy)

What is Vitamin D (25-Hydroxy)?

A Vitamin D (25-Hydroxy) test measures the level of vitamin D in the body. Vitamin D is a fat-soluble essential nutrient that helps the body absorb calcium & phosphorus to maintain strong bones & teeth and to have a healthy immune system. Vitamin D levels are a valuable indicator of many bone-related problems, such as rickets, osteomalacia, and osteoporosis.

Vitamin D is vital to many bodily functions, including immune system regulation, maintenance of bone health, and cell growth. It is also a multifunctional hormone that regulates the levels of nutrients like calcium and phosphorus. Vitamin D can be obtained from healthy exposure to sunlight. Additionally, dietary sources such as fortified foods, green vegetables, mushrooms, egg yolks, fatty fish, and vitamin D supplements can help the body maintain healthy levels of this nutrient.

As per an NCBI (National Center for Biotechnology Information) study, vitamin D deficiency is highly prevalent across all age groups in India. Insufficient vitamin D levels can increase susceptibility to fractures, weakened muscles, fatigue, compromised immune function, and a higher likelihood of chronic illnesses like diabetes. A Vitamin D (25-Hydroxy) examination can aid in assessing whether your body has an inadequate supply (deficiency) or an excessive amount of vitamin D, often resulting from excessive supplement intake. If such circumstances arise, it may be necessary to discontinue vitamin D supplements and seek medical advice.

Usually, no special preparation is required for this test; you may consume a regular diet before taking the test. However, it is generally recommended to stop taking vitamin D supplements before a Vitamin D (25-Hydroxy) test, as these supplements may affect the accuracy of the test results.

Test result ranges are approximate and may differ slightly between labs depending on the methodology and laboratory guidelines. Talk to your doctor about your specific test results. The test results will help them determine your medical condition, make recommendations for lifestyle modifications such as diet and exercise, prescribe medication if required to manage your condition, and formulate your overall treatment plan.

What is Vitamin D (25-Hydroxy) used for?

A Vitamin D (25-Hydroxy) test can be done:

To determine deficient, insufficient, or toxic vitamin D levels in the body.
For routine checkups in individuals at high risk of vitamin D deficiency. The risk of vitamin D deficiency increases with obesity, limited sun exposure, weight loss surgery, digestive disorders like Crohn’s disease, kidney or liver disease, and the use of certain medicines like phenytoin.
In individuals with vitamin D deficiency symptoms, such as bone deformities, immune system dysfunction, muscle cramps, and dental abnormalities.
To monitor the adequacy of treatment in patients who are receiving vitamin D supplements.
To diagnose/monitor problems with the functioning of the parathyroid gland since the parathyroid hormone (PTH) is essential for vitamin D metabolism.

What does Vitamin D (25-Hydroxy) measure?

A Vitamin D (25-Hydroxy) test measures the levels of vitamin D in the body. It is an essential nutrient that can be synthesized in the body upon healthy exposure to sunlight or absorbed from dietary sources. It majorly exists in two forms: Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol). Vitamin D2 is present in plants, such as yeast or mushrooms, and is available as a supplement in fortified foods, and vitamin D3 is found in foods like cheese, green vegetables, mushrooms, egg yolks, and fatty fish.

Both forms of vitamin D (D2 and D3) need to undergo some chemical changes before being available for use in the body. These chemical changes take place in the liver or kidneys. The liver converts vitamin D to 25-hydroxyvitamin D (25-OH vitamin D). A Vitamin D (25-Hydroxy) test measures the level of this 25-OH vitamin D as it is the primary form of vitamin D that circulates in the blood.

Interpreting Vitamin D (25-Hydroxy) results

Interpretations

A lower vitamin D level than the normal reference range indicates vitamin D deficiency, which can be because of less sun exposure, dietary lack, or decreased absorption from the intestine.

A higher vitamin D level than the normal reference range indicates vitamin D intoxication, usually due to excess vitamin supplementation.

Range:

The vitamin D range is measured as nanograms per milliliter (ng/mL) or nmol/L and can vary from lab to lab.

Level	Reference range (ng/mL)
Deficiency	<20
Insufficiency	20-29
Sufficiency	30-100
Toxicity	>100

Note:

This test does not include a separate vitamin D2 and D3 level analysis.
There can be seasonal variation in 25 (OH) vitamin D levels, with values being 40-50% lower in winter than in summer. It is also influenced by sunlight, latitude, skin pigmentation, sunscreen use, and hepatic function.
25 (OH) vitamin D levels can vary with age.
25 (OH) vitamin D level is increased during pregnancy.

Answers to Patient Concerns & Frequently Asked Questions (FAQs) about Vitamin D (25-Hydroxy)

Frequently Asked Questions about Vitamin D (25-Hydroxy)

Q. What are the signs and symptoms of low vitamin D levels?

Signs and symptoms of vitamin D deficiency may include fatigue, bone pain, depression, hair loss, muscle weakness, appetite loss, pale skin, and sleep disturbances.

Q. How much vitamin D is needed daily?

The recommended daily amount of vitamin D is 400 international units (IU) for children up to age 12 months, 600 IU for people aged 1 to 70 years, and 800 IU for people over 70 years. For adults with vitamin D levels below 30 ng/mL, the Endocrine Society guidelines recommend a daily intake of 1,500–2,000 IU to restore healthy vitamin D levels.

Q. What is the right time to get a vitamin D test done?

A vitamin D test can be done at any time of the day. However, you should stop taking vitamin D supplements before the test to get accurate results.

Q. Are there any risks associated with a vitamin D test?

No, usually, there are no risks associated with this test. The blood sample is withdrawn with the help of a needle, and the process is fairly fast and relatively painless. Very rarely, you may experience excessive pain, bleeding, hematoma (blood collection under the skin), bruising, or infection at the site of the needle prick. Consult the doctor if you experience any of these.

Q. What can cause vitamin D deficiency?

The major cause of vitamin D deficiency is insufficient sunlight exposure or a vitamin D-deficient diet.

Q. Who should be tested for Vitamin D?

Vitamin D 25 (OH) should be tested in individuals who are undergoing therapy to prevent or treat osteoporosis, patients having signs and symptoms of low calcium level (hypocalcemia) or high calcium level (hypercalcemia). It should also be done in patients with cystic fibrosis, Crohn’s disease, and with gastric bypass surgery, patients receiving vitamin D therapy who do not demonstrate clinical improvement. Along with that, these tests can be done in elderly people, especially those with minimal exposure to sunlight, children and adults with suspected rickets and osteomalacia, respectively, and infants who are exclusively breastfed.

Q. What are the additional lab tests needed to be performed in case of abnormal Vitamin D test results?

Additional tests that can help establish vitamin D deficiency include 24-hour urine calcium, parathyroid hormone total or bone alkaline phosphatase level, serum calcium, and serum phosphorus level.

Q. What is osteomalacia?

Osteomalacia is the softening of the bones due to demineralization (the loss of minerals) and, most notably, by the depletion of calcium from bone. It is a characteristic feature of vitamin D deficiency in adults. Osteomalacia can also be caused by poor dietary intake or poor absorption of calcium and other minerals needed to harden bones.

Q. What are the sources of Vitamin D?

Vitamin D is derived from endogenous sources and exogenous sources. Endogenous sources are produced in our body when our skin is exposed to sunlight. In contrast, exogenous sources can only be derived from other sources, as they are not made in our bodies. Dietary sources of vitamin D include fish, eggs, fortified dairy products, and nutritional supplements.

Q. What is osteoporosis?

Osteoporosis is a condition of fragile bones with increased susceptibility to fracture. Vitamin D and calcium deficiency are some of the leading causes of osteoporosis. Other risk factors can be genetics, lack of exercise, personal history of fracture as an adult, cigarette smoking, excessive alcohol consumption, history of rheumatoid arthritis, low body weight, and family history of osteoporosis. Usually, osteoporosis does not manifest itself until bone fractures occur. X-rays and bone mineral density tests can help diagnose osteoporosis.

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References

Vitamin D [Internet]. NIH; 12 Aug. 2022 [Accessed 11 Mar. 2023]. Available from: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

Aparna P, Muthathal S, Nongkynrih B, Gupta SK. Vitamin D deficiency in India. J Family Med Prim Care. 2018 Mar-Apr;7(2):324-330. [Accessed 11 Mar. 2023]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6060930/

Vitamin D [Internet]. Boston, USA: Harvard T.H. Chan; March 2023 [Accessed 11 Mar. 2023]. Available from: https://www.hsph.harvard.edu/nutritionsource/vitamin-d/