Vitamin D Test

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. Another type of vitamin D test measures a different form of vitamin D in your blood. It's called 'active vitamin D.' (It may also be called calcitriol or 1,25-dihydroxyvitamin D.) This test isn't usually used to check if you have enough vitamin D.

But it may be used to monitor kidney problems or to help find the cause of abnormal calcium levels in your blood.

Why this test is done

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

How to prepare

You don't need any special preparations for a vitamin D test. But be sure to tell your provider about all the medicines, vitamins, and supplements you take, because they may affect your test results. But don't stop taking any medicines unless your provider tells you to.

Sample type

Blood

Other names for this test

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