Vitamin D, 25-Hydroxy (Gold Standard) Test
A Vitamin D, 25-Hydroxy test measures 25-hydroxyvitamin D in the blood — the main circulating form of vitamin D, and the marker clinicians most often use to help evaluate a person's overall vitamin D status.
About this test
This test measures serum 25-OH vitamin D concentrations to assess circulating vitamin D activity and screen for deficiencies that can lead to bone diseases.
25-hydroxyvitamin D, the main form of vitamin D that circulates in the blood.
Who might consider this test?
- Exploring bone or muscle health, general fatigue, or aches without an obvious explanation
- Limited sun exposure, certain diets, or wanting to track vitamin D status over time
- Building a broader picture of calcium, bone, and muscle-related health alongside other markers
Test details
| Quest code | 17306 |
|---|---|
| Methodology | Immunoassay |
| Sample type | 0.8 mL serum |
| Patient preparation | Fast before your blood draw if you can; water is fine. |
| Collection | Quest patient service center |
Reference range
30-100 ng/mL
Reference ranges are general guidance. The range printed on your own laboratory report is the one that applies to your result.
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Additional details
Additional details
Vitamin D reaches the body in a few ways: it forms in the skin in response to sunlight, and it comes from certain foods and supplements. Once it enters the bloodstream, the liver converts it into 25-hydroxyvitamin D, the form this test measures. Because that form has a relatively long presence in the blood, it tends to reflect a person's stores built up over weeks rather than what happened on any single day.
The body carries vitamin D in more than one form. A different, active form exists as well, but it can shift for reasons unrelated to a person's true supply, so it is generally not the first choice for a status check — which is why the 25-hydroxy form is the one most clinicians reach for.
The test itself is a simple blood draw at a Quest patient service center. A phlebotomist collects a sample from a vein, usually in the arm, and it is sent to the laboratory. Quest lists preparation instructions for this test; they appear with the test details, and people follow any further instructions their ordering clinician provides. A clinician then reads the result in the context of symptoms, history, and anything else measured alongside it.
Vitamin D status can shift with the seasons and with where someone lives, since skin synthesis depends on how much sunlight is available and how intense it is. Skin tone, time spent outdoors, and use of sun protection all play a role too, which is part of why people with limited sun exposure often look into their vitamin D status in the first place. Dietary sources include fatty fish, fortified foods, and supplements, though how much any of these contribute varies from person to person.
Because the 25-hydroxy form changes gradually, a single result is a snapshot rather than a trend. Some people and their clinicians choose to recheck it after a season changes or after a change in habits, to see how the picture has moved. How often to repeat the test — if at all — is a decision for a clinician based on an individual's situation, not a fixed schedule.
Order online and a physician order is included — no doctor's visit and no insurance needed. Your sample is collected at a Quest Diagnostics patient service center.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does the Vitamin D, 25-Hydroxy test measure?
It measures 25-hydroxyvitamin D, the main circulating form of vitamin D. This form reflects the combined contribution of sunlight, food, and supplements and is the marker most often used to look at overall vitamin D status.
Why is this called the gold-standard vitamin D test?
The 25-hydroxy form is relatively stable and abundant in the blood, so it gives a dependable snapshot of a person's stores. That reliability is why clinicians most often choose it when assessing vitamin D status.
How is the sample collected?
Through a routine blood draw at a Quest patient service center. A phlebotomist takes a small sample from a vein in the arm and sends it to the laboratory for analysis.
Do I need to prepare for this test?
Fast before your blood draw if you can; water is fine. This is the preparation Quest publishes for this test; if your clinician gives you different instructions, follow theirs.
Can I interpret my vitamin D result on my own?
A result is best read by a clinician who can weigh it against symptoms, diet, sun exposure, and other markers. The results page is a starting point for that conversation rather than an answer on its own.
How much does the Vitamin D 25 Hydroxy test cost?
The cash price at Celio Health is $45. That covers the physician's order and sample collection at a Quest patient service center — no insurance is needed and there's no separate doctor's visit to pay for.