Test library
Vitamin D Deficiency Blood Test
The Vitamin D 25-Hydroxy test measures the main circulating form of vitamin D in the blood, known as calcidiol. It is used to check for low or elevated vitamin D levels and to support evaluation of bone, muscle, and immune health.
Order Vitamin D Blood 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 Blood Test- Typical turnaround
- 1-3 business days
- Starting price
- From $118
- Results
- Confidential, online
Quick answer
The Vitamin D 25-Hydroxy test is a blood test that measures calcidiol, the form of vitamin D the body stores and circulates. It is commonly ordered to check for low vitamin D, to monitor supplementation, or to evaluate symptoms that may relate to bone and muscle health. Results are interpreted by a qualified healthcare provider alongside diet, sun exposure, and other factors.
What this test measures
Vitamin D supports calcium absorption and helps maintain healthy bones and muscles. The body makes it when skin is exposed to sunlight and takes in additional amounts from certain foods and supplements. The liver converts vitamin D into 25-hydroxyvitamin D, also called calcidiol, which is the main form measured in blood. Because calcidiol reflects overall vitamin D stores, it is the preferred marker for assessing vitamin D status.
The test requires a single blood sample, usually drawn from a vein in the arm. The laboratory reports the calcidiol concentration, and clinicians compare it with reference ranges that vary by laboratory and by the group being tested. Vitamin D can also be assessed through related markers, but the 25-hydroxy form remains the standard for routine evaluation of deficiency or excess.
People may be tested when they have risk factors for low vitamin D, such as limited sun exposure, darker skin, older age, or conditions that affect fat absorption. It may also be ordered to monitor replacement therapy or to investigate bone pain, muscle weakness, or frequent fractures. A provider interprets the result with the person's history rather than in isolation.
- 25-Hydroxyvitamin D (calcidiol)
- Vitamin D2 (ergocalciferol)
- Vitamin D3 (cholecalciferol)
- Total 25-hydroxyvitamin D
- Calcium
- Phosphate
- Alkaline phosphatase
- Parathyroid hormone (PTH)
- Magnesium
- Albumin
Why people order this test
- Investigate suspected vitamin D deficiency
- Check vitamin D status when sun exposure is limited
- Monitor vitamin D replacement therapy
- Evaluate bone pain, muscle weakness, or frequent fractures
- Assess vitamin D absorption in digestive conditions
- Screen for low vitamin D before other evaluations
How to prepare
No fasting is usually required for a vitamin D blood test, though the laboratory may ask you to follow specific instructions if additional tests are ordered. A blood sample is collected from a vein.
Understanding your results
Results are generally available within one to three business days. The report shows the calcidiol level, which a qualified healthcare provider interprets against the appropriate reference range along with diet, sun exposure, and supplements.
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Frequently Asked Questions
What does the vitamin D 25-hydroxy test measure?
It measures calcidiol, the main circulating form of vitamin D. This form reflects the body's overall vitamin D stores and is the standard marker for assessing vitamin D status.
Do I need to fast before this test?
Fasting is not usually required. Follow any preparation instructions provided with the order, especially if other tests are included.
How long does it take to get results?
Results are typically available within one to three business days after the sample reaches the laboratory.
Can I take vitamin D supplements before the test?
Continue your usual routine unless the ordering provider says otherwise. Telling the provider about supplements helps with interpretation.
What does a low result mean?
A low calcidiol level suggests vitamin D insufficiency or deficiency. A healthcare provider can explain what it means in context and whether follow-up is needed.
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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