Vitamin D 25-Dihydroxy (Calcitriol) Test
Below is a plain-language overview of the vitamin d 25-dihydroxy (calcitriol) test. The Vitamin D 25-Dihydroxy (Calcitriol) Test measures the active form of vitamin D in your blood. It is usually ordered when a clinician suspects a problem with calcium regulation, parathyroid function, or kidney activation of vitamin D, rather than to check for a simple vitamin D deficiency.
- Sample type
- blood
- Category
- Vitamin & Mineral
- Turnaround
- 1-3 business days
- Price
- $170
- Referral
- Not required
The Vitamin D 25-Dihydroxy (Calcitriol) Test measures the active form of vitamin D in your blood. It is usually ordered when a clinician suspects a problem with calcium regulation, parathyroid function, or kidney activation of vitamin D, rather than to check for a simple vitamin D deficiency.
What it measures
- 25-dihydroxyvitamin D (calcitriol) — The active hormone form of vitamin D that helps control calcium and phosphate levels.
- Calcium — A mineral that works closely with vitamin D and parathyroid hormone.
- Phosphorus — Another mineral affected by vitamin D activity.
- Parathyroid hormone (PTH) — A hormone that rises or falls in response to calcium and vitamin D levels.
Who it is for
This test is typically ordered by endocrinologists, nephrologists, or other clinicians evaluating calcium disorders, kidney disease, or unusual vitamin D metabolism. It is not a routine screening test for most adults.
Preparation
No fasting is usually required. Tell your clinician about any vitamin D, calcium, or steroid supplements you take, because timing and recent doses can affect the result.
Results and what they mean
Results are reported as a number with a reference range, and your clinician interprets them alongside calcium, phosphorus, and PTH. A single value is rarely enough to make a decision. This is general information only and is not medical advice; discuss your results with a qualified clinician.
How to order this test
- Choose the test and place a confidential order online.
- Select a certified collection site and pick a time that suits you.
- Have your specimen collected — most draws take only a few minutes.
- Review results in a secure portal, typically within 1–3 days.
Preparation, hours, and pricing vary by site; confirm details directly with the lab before your visit.
Availability by state
Direct-access online ordering for the vitamin d 25-dihydroxy (calcitriol) test is available in most states. It is currently unavailable in 6 states:
Everywhere else you can order confidentially and collect your sample at a certified site. Browse by state →
Frequently asked questions
How is this different from a regular vitamin D test?
A regular vitamin D test measures 25-hydroxyvitamin D, the storage form. This test measures calcitriol, the active hormone form, which is used in more specific situations.
Do I need to stop my vitamin D supplement?
Ask your clinician. Do not stop or change any supplement or medication on your own before testing.
Can I eat before this test?
Yes, fasting is usually not required unless your clinician gives other instructions.
What if my result is outside the reference range?
Your clinician will consider your symptoms, other lab values, and medications before deciding what it means. Do not adjust treatment based on the number alone.