Vitamin D Test: When to Get It and How to Read It
The vitamin D test is a simple blood test called 25-hydroxy vitamin D. No fasting is required.
Vitamin D is checked with an ordinary blood test. On the report it appears as "25-hydroxy vitamin D" or "25(OH)D" — the stored form, which is why it is the one measured.
The ranges
| Category | Range (ng/mL) |
|---|---|
| Deficiency | Below 20 |
| Insufficiency | 20 – 29 |
| Sufficient | 30 and above |
Ranges vary slightly between laboratories, so always read the range printed on your own report.
Who should be tested
- Long-standing tiredness, or bone and muscle pain
- A life with very little sun exposure
- A fracture, or evidence of weak bones
- Gut conditions that affect absorption
- A previous deficiency, after finishing treatment
Routine testing in people with no symptoms or risk factors is generally not considered necessary — your doctor decides.
Preparation
Nothing particular. Fasting is not required. If other tests are being done at the same time, follow the laboratory’s advice. Tell your doctor if you are taking supplements, since they affect the result.
Retesting after treatment
Where a deficiency is found, doctors usually retest a few months after treatment to see whether levels have improved. Retesting too soon does not give a useful picture.
Frequently asked questions
Do I need to fast for it?+
No, fasting is not required for this test.
Will the result be accurate if I am taking supplements?+
It can read higher because of them, so tell your doctor what you are taking.
When should I retest after treatment?+
Your doctor decides, usually a few months after the course finishes.
Should I get tested without any symptoms?+
Routine testing without symptoms or risk factors is generally not considered necessary.