The Vitamin D test is a diagnostic assay that measures the levels of vitamin D present in the blood. Vitamin D, a fat-soluble vitamin, is a vital nutrient for people of all age groups and involved in numerous key functions in the human body. The biological roles of vitamin D comprise promoting calcium uptake by osteocytes for strong bones and joints, fortifying teeth, boosting immunity, elevating nervous system activity, ensuring brain power, maximal lung capacity and augmented heart health. Vitamin D also augments kidney functions, uplifts liver wellness by maintaining proper pH of blood, aside from controlling thyroid gland operations.

Also Read: Vitamin D: Functions, Food Sources, Deficiencies And Toxicity

Vitamin D Test and test tube

Vitamin D deficiency causes a host of health anomalies, such as bone-related disorders of osteoporosis, arthritis, liver ailments, excessive hair fall, skin infections, rickets, muscle cramps and illnesses pertaining to the nervous system like depression, schizophrenia and multiple sclerosis. It is hence important to determine the levels of vitamin D in an individual, particularly if symptoms of bone diseases, skin and hair problems and brain-related conditions are experienced. This helps to detect any instance of deficiency and take corrective steps to rectify the condition by getting adequate exposure under the sun and taking the required dose of vitamin D supplements.

What Is The Vitamin D Test?

The vitamin D test is fundamentally a blood test that calculates the concentrations of the by-product of vitamin D assimilation i.e. 25-hydroxyvitamin D, in the human body. There are two forms of vitamin D essential for human nutrition – vitamin D2, which is obtained from food sources and vitamin D3, that is synthesized upon direct exposure to sunlight and is also called the “sunshine vitamin”.

In the human system, both these compounds are converted into 25-hydroxyvitamin D or calcidiol that is distributed in the blood. The vitamin D test calculates the concentration of 25-hydroxyvitamin D, to determine if the person had adequate amounts of vitamin D or is deficient in the nutrient.

How Is The Vitamin D Test Done?

In the diagnostic centre, physician’s clinic or hospital, the doctor, nurse or certified lab pathologist draws a sample of blood from the individual for the purpose of the vitamin D test. The procedure of the vitamin D test is rather simple and straightforward, wherein a sterile injection is used to obtain blood from a vein in one of the arms. Once the blood is collected, a bandage is put on the site of the piercing and some pressure is applied, to prevent further bleeding. Usually, the bleeding ceases very quickly and the bandage can be removed after a few hours of drawing blood.

The blood sample for the vitamin D test can be collected at any time of the day and it is not required for the patient to provide their blood on fasting. Generally, there are no side effects or harmful consequences from the vitamin D test. The patient might sometimes experience a headache, dizziness or minor infection, swelling at the site of pricking. For kids and infants, a slight prick in the finger is sufficient to obtain enough blood for the vitamin D test.

Who All Should Get The Vitamin D Test?

The vitamin D test is recommended for those who have a high risk of nutrient deficiency, including people with obesity, elderly above the age of 60 and those who live in places that do not receive much direct sunlight. Also, people who have had any gastric bypass surgeries and chronic gastrointestinal disorders that hamper nutrient absorption in the body are advised to take the vitamin D test to probe for deficiency.

Also Read: Vitamin D Deficiency: Causes, Symptoms And Treatment

Moreover, any individual with any symptoms of bone disorders, muscle pain, nervous system conditions or skin and hair issues are also advised to take the vitamin D test, to confirm if they are deficient or not. The vitamin D test can also be done for normal, healthy adults to monitor the levels of the vital nutrient in the body.

What Do The Results Of The Vitamin D Test Signify?

The amount of 25-hydroxyvitamin D in blood implies whether the person is deficient, has adequate or very high levels of vitamin D in their body. When vitamin D test results are below 12 ng/mL (nanograms of 25-hydroxyvitamin-D per millilitre of blood), the person is said to be massively deficient. When the blood levels of vitamin D are in the range of 12ng/mL to 20 ng/mL, it still indicates lower than required levels of the nutrient.

Vitamin D concentrations between 20 ng/mL and 50 ng/mL are considered to be normal and the person is said to have a healthy vitamin D status. Reading above 50 ng/mL are very high levels of vitamin D, which could also lead to certain complications and need to be balanced.

Generally, when the person is determined to be deficient in vitamin D, the doctor prescribes vitamin D supplements in the appropriate doses, to bring the levels of the crucial nutrient to normal. They also advise the individual to eat a balanced diet and to expose themselves under the sun daily for a short period of time.


The vitamin D test is a very useful assay to determine if the person is deficient in vitamin D, which is an essential nutrient that performs many key functions in the body, particularly strong bones and teeth, optimal brain power, better immunity and hormonal balance. It is advised to consult with a doctor after taking a vitamin D test, to ensure taking only the required correct doses of the supplements if found to be deficient and also to know if any additional tests might be necessary to detect any bone disorders if presenting with such symptoms.