Vitamin D3 Test

Vitamin D3 Test helps your body absorb calcium and maintain strong bones throughout your entire life. Your body produces vitamin D when the sun’s UV rays contact your skin. Other good sources of the vitamin include fish, eggs, and fortified dairy products. It’s also available as a dietary supplement.

Vitamin D must go through several processes in your body before your body can use it. The first transformation occurs in the liver. Here, your body converts vitamin D to a chemical known as 25-hydroxyvitamin D, also called calcidiol.

The test is also known as the 25-OH vitamin D test and the calcidiol 25-hydroxy cholecalciferol test. It can be an important indicator of osteoporosis (bone weakness) and rickets (bone malformation).

Why is a 25-hydroxy vitamin D3 test done?

Your doctor may request a 25-hydroxy vitamin D test for several different reasons. It can help them figure out whether too much or too little vitamin D is causing bone weakness or other abnormalities. It can also monitor people who are at risk of having a vitamin D deficiency.

Those who are at high risk of having low levels of vitamin D include:

• people who don’t get much exposure to the sun
• older adults
• people with obesity
• babies who are breastfed only (formula is usually fortified with vitamin D)
• people who have had gastric bypass surgery
• people who have a disease that affects the intestines and makes it difficult for the body to absorb nutrients, such as Chronis disease

What is it used for?

If you have a known bone disorder or a problem absorbing calcium, a vitamin D test may be used to see if a lack of vitamin D is causing your condition. Your provider may order a Vitamin D test if you have:

• Osteomalacia, soft bones, often with muscle weakness
• Low bone density, which can lead to osteoporosis.
• Rickets, a problem with bone growth in children

Because vitamin D can affect many parts of your body, you may have your vitamin D level checked if you have other chronic (long-term) medical conditions. Ask your provider if you should be tested.

Purpose of the test

Vitamin D testing is used to determine whether you have enough vitamin D in your body to support normal bodily functions. An inadequate level of vitamin D is called a deficiency. A more mild lack of vitamin D can be referred to as an insufficiency.

Your health care provider may order a vitamin D test to:

• Screen for a possible deficiency or insufficiency, if you have a risk factor that increases the likelihood of having a low level of vitamin D. A risk factor, is anything that makes it more likely for a health problem to occur.
• Diagnose a vitamin D deficiency or insufficiency if you have symptoms that suggest low levels. Testing may also be used to diagnose a rare vitamin D toxicity due to excess intake of vitamin D supplements.
• Monitor your vitamin D levels if you are being treated for a previously detected deficiency.

How to Prepare for the Test

Usually, you will not need to fast. However, this depends on the laboratory and the testing method used. Follow any instructions for not eating before the test. 

Evaluating the results of a 25-hydroxy vitamin D test

Results will depend on your age, sex, and the testing methods used. Results can also slightly vary from lab to lab.

According to the Office of Dietary Supplements (ODS) Source, levels of vitamin D are measured by the 25-hydroxy level in nanomoles/liter (nmol/L) or nanograms/milliliter (ng/mL). The results can indicate the following:

• deficiency: less than 30 nmol/L (12 ng/mL)
• potential deficiency: between 30 nmol/L (12 ng/mL) and 50 nmol/L (20 ng/mL)
• normal levels: between 50 nmol/L (20 ng/mL) and 125 nmol/L (50 ng/mL)
• high levels: higher than 125 nmol/L (50 ng/mL)

If your vitamin D levels are low and you’re having symptoms of bone pain, a doctor may recommend a special scan to check bone density. Doctors use this painless scan to evaluate a person’s bone health.

Low blood levels of 25-hydroxy vitamin D usually mean one (or more) of the following:

• you aren’t eating a balanced, complete diet
• your intestines aren’t absorbing the vitamins properly
• you’re not spending enough time outside to absorb adequate vitamin D levels through sun exposure

Some evidence links vitamin D deficiency to a higher risk of certain cancers, immune diseases, and cardiovascular disease.

High vitamin D blood levels generally result from taking too many vitamin pills and other nutritional supplements. High doses of vitamin D can result in a condition called hypervitaminosis D. Hypervitaminosis is a rare but serious condition that could put you at risk for liver or kidney problems.

High levels are rarely due to consuming too much of the vitamin through foods or sun exposure.

Your doctor will help explain the results of your test and determine if you have a vitamin D deficiency.

levels of vitamin D are measured by the 25-hydroxy level in nanomoles/liter (nmol/L) or nanograms/milliliter (ng/mL). The results can indicate the following:

• deficiency: less than 30 nmol/L (12 ng/mL)
• potential deficiency: between 30 nmol/L (12 ng/mL) and 50 nmol/L (20 ng/mL)
• normal levels: between 50 nmol/L (20 ng/mL) and 125 nmol/L (50 ng/mL)
• high levels: higher than 125 nmol/L (50 ng/mL)

Normal Results

The normal range of vitamin D is measured as nanograms per milliliter (ng/mL). Many experts recommend a level between 20 and 40 ng/mL. Others recommend a level between 30 and 50 ng/mL.

Many people are confused by the way these tests are reported.

• 25 hydroxy vitamin D3 (cholecalciferol) is the vitamin D that your own body has made or that you absorbed from an animal source (such as fatty fish or liver) or a cholecalciferol supplement.
• 25 hydroxy vitamin D2 (ergocalciferol) is the vitamin D that you have absorbed from foods fortified with plant vitamin D or from an ergocalciferol supplement.
• The two hormones (ergo- and cholecalciferol) work similarly in the body. The important value is the total 25 hydroxy vitamin D levels in your blood.

What Abnormal Results Mean

A lower-than-normal level can be due to a vitamin D deficiency, which can result from:

• Lack of skin exposure to sunlight, darkly pigmented skin, or consistent use of high-SPF sunscreen
• Lack of enough vitamin D3 Tests in the diet
• Liver and kidney diseases
• Poor food absorption
• Use of certain medicines, including phenytoin, phenobarbital, and rifampin
• Poor vitamin D3 Test absorption due to advanced age, weight-loss surgery, or conditions in which fat is not absorbed well

A higher-than-normal level may be due to excess vitamin D, a condition called hypervitaminosis D. This is most commonly caused by taking too much vitamin D. It can result in too much calcium in the body (hypercalcemia). This leads to many symptoms and kidney damage.

Are there any risks to the test?

There is very little risk of 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