Vitamin D

Also written as: 25-hydroxyvitamin D, 25(OH)D

The storage form of vitamin D, used to assess vitamin D status.

What it measures

The concentration of 25-hydroxyvitamin D, the form that circulates and is used to judge overall vitamin D status.

Why a doctor orders it

Checked when bone health, deficiency symptoms, malabsorption, or certain chronic conditions are being considered. Routine screening in people without risk factors is debated among expert bodies.

What is generally associated with a higher result

Higher values are almost always from supplementation. Very high values from prolonged high-dose supplements can raise calcium.

What is generally associated with a lower result

Broadly associated with limited sun exposure, darker skin, older age, obesity, malabsorption conditions, and some medications.

Everyday things that move this number

Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:

Season and latitude
Sun exposure
Supplement use and timing
Body weight

Questions to take to your appointment

Do I have a reason to be tested for this, or was it routine?
If supplementing, what dose and for how long before rechecking?

Build a printable questionnaire with your own results →

Where to read more

MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .

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