Vitamin D (25-OH)
Also called: Vitamin D, 25-OH Vitamin D, 25(OH)D
25-hydroxyvitamin D is the storage form of vitamin D and the standard way to measure your vitamin D status.
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What does Vitamin D (25-OH) measure?
Vitamin D is produced when sunlight hits your skin and is absorbed from a small set of foods (fatty fish, fortified dairy). The kidneys convert it to its active form, but the storage form — 25-hydroxyvitamin D — is what blood tests measure because it reflects long-term intake and sun exposure rather than today's snapshot. Vitamin D status affects calcium absorption, bone density, muscle strength and a long list of associations with immune and cardiovascular health that are still under active study.
What does a high Vitamin D (25-OH) level mean?
- Over-supplementation — almost always the cause; very high values can drive hypercalcaemia.
- Granulomatous diseases — sarcoidosis, some lymphomas (rare).
What does a low Vitamin D (25-OH) level mean?
- Limited sun exposure — northern latitudes, indoor lifestyle, heavy sunscreen use, dark skin pigmentation.
- Malabsorption — coeliac disease, Crohn's, gastric bypass.
- Obesity — vitamin D distributes into adipose tissue, lowering serum levels.
- Chronic kidney or liver disease — reduced conversion.
When to discuss with a doctor
Levels below 20 ng/mL meet the deficiency threshold most clinicians act on with supplementation; below 30 ng/mL is the insufficient zone where many guidelines also recommend a course. Mediora.AI surfaces your reading against these thresholds. Discuss dose and duration with your clinician — high-dose self-supplementation without monitoring carries a hypercalcaemia risk.
Related markers
Commonly confused with
- Calcitriol (1,25-dihydroxyvitamin D) Calcitriol is not another vitamin D test. The usual test measures the storage form, which shows your reserves; calcitriol is the active hormone the kidneys make from it, and it is ordered for kidney and calcium problems, not to check your levels.