Vitamin D helps your body use calcium and keep bones strong. The blood test measures 25-hydroxy vitamin D, the form that shows how much your body has stored.
Experts do not fully agree on the best level. Some labs mark anything under 30 ng/mL as low, while major health bodies say 20 ng/mL is enough for most people. That is why your report and your doctor may describe the same number differently.
Every lab sets its own normal range, based on its equipment and the people it tests. Always compare your result with the range printed on your own report.
Why this test is done
- Bone health, falls or fractures
- Little sun, darker skin, covering clothing, or living far from the equator
- Conditions or medicines that affect how vitamin D is absorbed
What each result means
25-hydroxy vitamin D(25(OH)D, calcidiol)
Your body's stored vitamin D.
Typical adult range: Below 12 ng/mL (30 nmol/L) is deficient. 12 to 20 ng/mL (30 to 50 nmol/L) may be too low for bone health. 20 ng/mL (50 nmol/L) or more is enough for most people. Above 50 ng/mL (125 nmol/L) may be too high.
If high: Almost always from taking high-dose supplements. Very high levels can raise calcium in the blood.
If low: Common, especially in winter. Low levels over time can weaken bones. Your doctor may suggest a supplement and a dose.
Before the test
- No fasting needed.
- To convert: ng/mL multiplied by 2.5 gives nmol/L.
Questions to ask your doctor
- Is my level low enough to need a supplement, and what dose?
- Should my calcium be checked too?
- When should I test again?
When to get help fast: Very high vitamin D with nausea, vomiting, confusion, a lot of thirst or passing a lot of urine needs prompt medical care. In an emergency, call your local emergency number.
Sources
- MedlinePlus: Vitamin D Test
- NIH Office of Dietary Supplements: Vitamin D fact sheet
- MedlinePlus: Vitamin D
This guide is general information written in plain words. It is not medical advice and has not been reviewed by a doctor for your situation. Read our medical disclaimer.