A vitamin D test measures the levels of vitamin D in your blood.  Vitamin D helps your body absorb calcium to build healthy bones and teeth. It also helps keep your muscles, nerves, and immune system working normally. Having Vitamin D deficiency (very low levels of vitamin D) can lead to bone disorders and other medical conditions.

You can get vitamin D from three sources:

• Sunlight. Your body makes vitamin D when your bare skin, without sunscreen, is exposed to sunlight when you are outdoors.
• Certain foods. Only a few foods, such as egg yolks, liver, and fatty fish, naturally contain vitamin D. That's why vitamin D is added to many foods, including breakfast cereals, milk, and other dairy items.
• Supplements. You can take vitamin D supplements in pill form or liquid drops.

Before your body can use vitamin D, your liver must change it into another form called 25 hydroxyvitamin D, or 25(OH)D. Most vitamin D blood tests measure the level of 25(OH)D in your blood because that's the most accurate way to see if you have enough vitamin D.

Other names: 25-hydroxyvitamin D, 25(OH)D, cholecalciferol test, ergocalciferol test, calcidiol test, vitamin D2 test, vitamin D3 test

A vitamin D test is used to check the levels of vitamin D in your blood. The test is usually done if your health care provider thinks that a bone or other health condition you have could be caused by very low vitamin D levels.

Routine vitamin D testing is not recommended for everyone. Your provider can let you know whether a vitamin D test is right for you.

Your provider may order a vitamin D test if you:

·         Have been diagnosed with a medical condition that may be related to vitamin D deficiency, such as:

·         Osteomalacia, soft bones, often with muscle weakness

·         Low bone density, osteopenia, or osteoporosis

·         Rickets, a problem with bone growth in children

·            Have signs or symptoms of a condition that may be related to vitamin D deficiency such as:

·         Bone pain

·         Muscle weakness or aches

·         Soft or deformed bones

·         Weak bones and fractures (broken bones)

·         Have a high risk for developing vitamin D deficiency. Your risk may be high if you:

·         Rarely expose your skin to sunlight because you stay indoors, cover up outside, use sunscreen, or live where there is little sunlight

·         Don't eat enough food or have malnutrition

·         Have had weight loss surgery

·         Have a condition that makes it difficult to absorb nutrients in food, such as Crohn's disease, ulcerative colitis, or celiac disease

·         Have kidney or liver disease that affects your ability to change vitamin D into a form your body can use

·         Take medicines that affect vitamin D levels, including certain statins to lower cholesterol, steroids, and weight-loss medicines

Babies and children can develop serious health problems from a lack of vitamin D. A provider may order a vitamin D test for:

·         Babies that are mainly fed breastmilk. Breastmilk is low in vitamin D. All babies need vitamin D supplements shortly after birth, unless they are fed only formula, which contains vitamin D.

·         Children with diets low in vitamin D.

If you are taking vitamin D supplements for vitamin D deficiency, your provider may order a test to see if your vitamin D levels are improving.

Getting too much vitamin D from supplements can harm your health. This rarely happens, but if you take supplements and have symptoms of high levels of vitamin D, your provider may order a test. The symptoms of too much vitamin D include:

·         Nausea and vomiting

·         Poor appetite

·         Constipation

·         Muscle weakness

·         Weight loss