The vitamin D test may be ordered as part of health checkup, or to evaluate a person when having abnormal blood levels of calcium, phosphorus, and/or parathyroid hormone level as well as when having evidence of bone disease or bone weakness. In addition, vitamin D ordered on the people at high risk of vitamin D deficiency include the elderly or obese people, people who don't get enough sun exposure and people with darker skin.

The 25-hydroxyvitamin D test in serum is preferred as the initial test for assessing vitamin D status and reflect body stores.

Moreover, vitamin D test is performed as a second-order test in the assessment of vitamin D status, especially in patients with renal disease and prior to starting drug treatment for osteoporosis.

The vitamin D test does not need any preparation steps by the patient. Besides, the patient should tell the healthcare provider about all of the drugs or supplements in use, since certain drugs may increase the vitamin D in the blood.

Reference values

*Normal ranges may vary from one lab to another due to several factors, so it is important to discuss test results with a doctor .

Interpretation:

The level of 25-hydroxyvitamin D is decreased in people who are not having adequate exposure to sunlight, or not eating the right amount of food containing vitamin D, or having a problem in absorbing the vitamin from the stomach. Whereas, a high level of 25-hydroxyvitamin D indicates excessive vitamin pills or other supplements.

Furthermore, a 1,25-dihydroxyvitamin D level decreases in some conditions like chronic renal failure and hypoparathyroidism. On the other hand, 1,25-dihydroxyvitamin D level increases in sarcoidosis and other granulomatous diseases as well as in some malignancies, primary and also physiologic hyperparathyroidism. 

A high concentration of vitamin D in the body can lead to vitamin toxicity. There are some symptoms of vitamin D toxicity like nausea, loss of appetite, vomiting, polyuria, muscle weakness, and constipation.  

There are some drugs that may increase vitamin D levels including etidronate disodium and pravastatin. Besides, there are Drugs and substances that may reduce vitamin D levels include aluminum hydroxide, anticonvulsants, cholestyramine, colestipol, glucocorticoids, isoniazid, mineral oil, and rifampin.

The test is performed by drawing a blood sample from the patient’s arm to analyze and measure the amount of vitamin D in the sample of (1 mL) volume. The method most probably used is high-performance liquid chromatography.

A vitamin D test may be requested as part of a health checkup, or to assess the person when there are abnormal blood levels of calcium, phosphorous, and/or thyroid hormone as well as when there is evidence of bone disease or bone weakness. Additionally, vitamin D test is ordered for people at risk of developing vitamin D deficiency includes the elderly or obese, people who are not exposed enough to the sun and people with dark skin.

When a vitamin D deficiency is present, a healthcare practitioner recommends monitoring vitamin D deficiency treatment. In addition to, educating patients about the sources of food rich in vitamin and the importance of sunlight.

Vitamin D plays an important role in regulates the amount of calcium, phosphorus, and magnesium that are important in the growth and health of bone as well as teeth and muscles.

There are two active forms of vitamin D. The first form is ergocalciferol (vitamin D2) which that comes through ingested foods, and the other form is cholecalciferol (vitamin D3) is produced when the skin is exposed to sunlight.

The level of 25-hydroxyvitamin D is decreased or increased due to many reasons such as lack of exposure to sunlight, not eating the right amount of food containing vitamin D, or excessive vitamin pills or other supplements.

The level of 1, 25-dihydroxyvitamin D is decreased or increased in conditions like chronic renal failure and hypoparathyroidism, sarcoidosis, and other granulomatous diseases. A high concentration of vitamin D in the body can lead to vitamin toxicity.

The Endocrine Society defines vitamin D deficiency as a 25-hydroxyvitamin D blood level below 20 ng/mL (50 nmol/liter), and the level between 21–29 ng/mL (52.5–72.5 nmol/liter) of vitamin D insufficiency.

The U.S. Institute of Medicine reports that a 25-hydroxyvitamin D level of 20 ng/mL (50 nmol/liter) or higher is appropriate for bone health.