Test library
Active Vitamin D Test
This test measures a dihydroxy form of vitamin D in the blood. It is ordered to investigate low calcium and to monitor vitamin D metabolism in kidney disease, where activation of the vitamin can be impaired.
Order Vitamin D 25-Dihydroxy (Calcitriol) Test
Order online and visit a local collection site, or choose an at-home kit where available. No referral and no insurance required.
Order Vitamin D 25-Dihydroxy (Calcitriol) Test- Typical turnaround
- 1-3 business days
- Starting price
- From $170
- Results
- Confidential, online
Quick answer
The vitamin D 25-dihydroxy test measures a hydroxylated form of vitamin D in the blood. Vitamin D is activated through steps in the liver and kidneys, and the active form helps regulate calcium and phosphate. This test is used when low calcium is being investigated or when kidney disease may be affecting vitamin D metabolism. It uses a blood sample and is interpreted with related tests.
What this test measures
Vitamin D exists in several forms in the body. The most commonly measured form for routine status is 25-hydroxyvitamin D, while the fully active form, often called calcitriol or 1,25-dihydroxyvitamin D, is produced mainly in the kidneys. The active form controls the absorption of calcium and phosphate from the gut and their handling in bone and kidney.
Because activation depends on the kidneys, people with chronic kidney disease may not convert vitamin D to its active form efficiently. In that setting, measuring an active metabolite helps clinicians understand calcium balance. The test is also used when low calcium or abnormal phosphate levels need evaluation.
Results are not interpreted alone. Clinicians usually review them with calcium, phosphate, parathyroid hormone, and kidney function tests. A single value can be affected by kidney and liver function, other medications, and overall vitamin D status, so context is essential.
- Dihydroxyvitamin D (active vitamin D metabolite)
- Calcitriol level
- Serum calcium
- Phosphate
- Parathyroid hormone (PTH)
- 25-hydroxyvitamin D when paired
- Creatinine and estimated glomerular filtration rate when included
Why people order this test
- Investigate low calcium levels
- Monitor vitamin D metabolism in kidney disease
- Evaluate abnormal phosphate or parathyroid results
- Follow a known disorder of calcium regulation
- Assess vitamin D activation after kidney or liver changes
- Clarify results when routine vitamin D testing needs context
How to prepare
Fasting may be requested depending on which tests are bundled with the order. A blood sample is drawn from a vein, typically at the arm. Follow the collection and timing instructions provided with the order.
Understanding your results
Results are typically available within one to three business days. The report shows the active vitamin D level and is interpreted with calcium, phosphate, parathyroid hormone, and kidney function. A healthcare provider explains what the combined findings indicate.
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Frequently Asked Questions
What is the difference between vitamin D forms?
25-hydroxyvitamin D is the main storage form used for routine testing. The active form, often called calcitriol, is produced mainly in the kidneys and regulates calcium.
Why is this test used in kidney disease?
The kidneys activate vitamin D. When kidney function is reduced, activation can be impaired, so measuring an active metabolite helps assess calcium balance.
Is this the same as a routine vitamin D test?
Not exactly. Routine screening usually measures 25-hydroxyvitamin D. This test measures a different, active form used in more specific situations.
Do I need to fast before the test?
Fasting may be needed if other tests in the same order require it. Follow the instructions supplied with your order.
Which other tests are usually reviewed with this one?
Calcium, phosphate, parathyroid hormone, and kidney function tests are commonly reviewed together with vitamin D results.
Ready to get tested?
Order online and visit a collection site near you, or choose a mail-in kit. No referral and no insurance required.
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Every page on this site is reviewed for clarity, sourcing, and accuracy. We update our library as testing options, collection networks, and accreditation standards change.