Vitamin D test
25-OH vitamin D · vitamin D blood test · calcidiol test
A blood test from a vein. It shows how much vitamin D is stored in your body.
For weakness, bone pain, frequent fractures, or osteoporosis, or when you take vitamin D, to choose the right dose.
⏱ Duration: the blood draw usually takes 5 minutes
Be sure to tell your doctor
How to prepare
- Food. The test is usually done in the morning on an empty stomach, or 3 to 4 hours after eating. Check with the lab.
- Water. You can drink plain water.
- Vitamins. Do not stop taking vitamin D on your own before the test. Tell your doctor what you take. The doctor decides.
What to bring
- Your referral, if you have one
- Past results, for comparison
How it goes
- You sit down, and your arm rests on the armrest
- A band is tightened above your elbow
- The skin is wiped with alcohol, and blood is taken from a vein
- The needle is removed, and a cotton pad is pressed on the spot
What you'll feel
- A quick needle prick for a couple of seconds
Afterwards
- Keep the cotton pad pressed for a few minutes
- You can eat right away
- Results usually come in 1 to 3 days
- Your doctor will explain what the numbers mean
Common questions
Do I need to fast for a vitamin D test?
Strict fasting is usually not required. But many labs ask you to come in the morning on an empty stomach, or 3 to 4 hours after eating.
Can I take vitamin D without a test?
A preventive dose is often given without a test. A treatment dose is best chosen with your doctor, based on the test.