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 functioning properly. Having a 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 produces vitamin D when your bare skin, without sunscreen, is exposed to sunlight when you are outside.
• Some 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 products.
• Supplements. You can take vitamin D supplements in the form of pills or liquid drops.

Before your body can use vitamin D, your liver has to turn 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 it is the most accurate way to check 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 is not usually used to check if you have enough vitamin D. But it can be used to monitor kidney problems or to help find the cause of abnormal levels of calcium in your blood.

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 vitamin D levels in your blood. The test is usually done if your health care provider thinks that a bone condition 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 if a vitamin D test is appropriate for you.

Your provider may request a vitamin D test if you:

• Have been diagnosed with a medical condition that may be linked to vitamin D deficiency, such as:
  • Osteomalacia, soft bones, often with muscle weakness
  • Low bone density, osteopenia, or osteoporosis
  • Rickets, a bone growth problem in children
• Have signs or symptoms of a condition that may be linked to vitamin D deficiency, such as:
  • Bone pain
  • Muscle weakness or pain
  • Soft or deformed bones
  • Fragile bones and fractures (broken bones)
• Have a high risk of developing vitamin D deficiency. Your risk may be high if you:
  • Rarely expose your skin to the sun because you stay inside, cover up outside, use sunscreen, or live in a place where there is little sunlight
  • Do not eat enough or are malnourished
  • Have you had weight loss surgery
  • Have a condition that makes it difficult to absorb nutrients from food, such as Crohn's disease, ulcerative colitis, or celiac disease
  • Have kidney or liver disease that affects your ability to turn vitamin D into a form that your body can use
  • Taking medications that affect vitamin D levels, including some statins to lower cholesterol, steroids, and medications for weight loss

Babies and children can develop serious health problems due to a lack of vitamin D. A provider may request a vitamin D test to:

• Babies who are primarily fed breast milk. Breast milk is low in vitamin D. All babies need vitamin D supplements soon after birth, unless they are only fed formula, which contains vitamin D.
• Children with a diet 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 be harmful to your health. This rarely happens, but if you are taking supplements and have symptoms of high vitamin D levels, your provider may request a test. Symptoms of excess vitamin D include:

• Nausea and vomiting
• Bad appetite
• Constipation
• Muscle weakness
• Weight loss

You don't need any special preparations for a vitamin D test, but be sure to talk to your provider about any medications, vitamins, and supplements you take, as they may affect your test results. But don't stop taking medication unless your provider asks you to.

There is very little risk in taking a blood test. You may feel a slight pain or bruise where the needle was inserted, but most symptoms go away quickly.

Your test results can be reported as “total vitamin D,” or as the amounts of vitamin D2 and vitamin D3. Vitamin D2 and D3 work in much the same way in your body. If you add vitamin D2 and D3 together, you get your total vitamin D. Total vitamin D is the important number to check.

Your test results will generally describe total vitamin D levels as:

• Deficient, which means very low vitamin D levels that can affect your bones and overall health
• Insufficient, which means low vitamin D levels that can weaken your bones and affect your health, even if you don't have symptoms
• Sufficient or optimal, which means vitamin D levels that are sufficient for good bone and general health for most people
• Toxic or possible toxicity, which means very high vitamin D levels that could cause health problems

If your total vitamin D levels are deficient or insufficient, this may mean that you:

• Don't get enough vitamin D from your diet and/or sun exposure
• Have difficulty absorbing vitamin D from your food, which may be a sign of a malabsorption disorder
• Have trouble converting vitamin D into a form that your body can use, which may be a sign of kidney or liver disease
• Taking medication that affects vitamin D levels

To increase your vitamin D levels, your provider may recommend taking vitamin D supplements and/or eating more vitamin D rich foods. This is generally safer than getting more sunlight, which can cause skin cancer.

If your total vitamin D levels are high or toxic, it usually means you're getting too much through supplements. You'll need to stop taking supplements to lower your vitamin D levels. This is because excess vitamin D can cause serious damage to your organs and blood vessels.

To understand what your vitamin D test results mean, talk to your provider.

Learn more about lab tests, reference ranges, and understanding results.

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