Vitamin D Test

This blood test measures 25-hydroxyvitamin D, the storage form that best reflects how much vitamin D the body actually has. It is ordered when deficiency is suspected for a reason, and routine testing of everyone is not recommended.

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What it is

Vitamin D exists in the body in several forms, and this test targets one of them: 25-hydroxyvitamin D, usually written 25(OH)D. That form is measured because it is the one that reflects overall stores, from sunlight, diet and supplements combined, rather than the short-lived active form the body regulates minute to minute. The result speaks to whether there is enough vitamin D on hand for the body to absorb calcium and maintain bone, muscle and nerve function. MedlinePlus notes that routine vitamin D testing is not recommended for everyone, which is unusual to say about a common blood test and is the key thing to know about this one.

Why it is done

  • To investigate bone pain, muscle weakness or a bone condition such as osteoporosis or rickets where low vitamin D could be the explanation
  • To check people at higher risk of deficiency, including those with very limited sun exposure or with conditions that impair absorption
  • To monitor someone taking vitamin D supplements, where the question is whether the dose has moved the level
  • To follow up on an abnormal calcium or bone result found on other testing

What to expect

A single blood draw from the arm, with no fasting and no preparation. Most laboratories return the result within a few days. Because vitamin D stores change slowly, a repeat test is usually spaced by months rather than weeks. Levels vary with the season and with sun exposure, so the time of year the sample was taken is part of how a clinician reads the number.

Questions worth asking

  • What diagnosis is this being ordered under? Coverage for vitamin D testing is frequently limited to specific conditions, and a screening order can be denied outright.
  • If coverage is uncertain, will the lab ask me to sign a form accepting responsibility for the cost, and what is the cash price if it does?
  • Was a single 25-hydroxyvitamin D test ordered, or a more expensive assay that separates the D2 and D3 forms?
  • If a recheck is planned after starting a supplement, how far out is it and will that second test be covered?

What Vitamin D Test costs by state

Vitamin D Test prices at hospitals

See every published price for Vitamin D Test: the full national range, the state and hospital breakdowns, and which hospitals charge the least.

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Sources

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