Vitamin D (D2, D3) QuestAssureD 25-Hydroxy Test
The Vitamin D (D2, D3) QuestAssureD 25-Hydroxy test measures 25-hydroxyvitamin D in the blood and reports the D2 and D3 forms separately. It is used to help evaluate a person's overall vitamin D status.
About this test
Vitamin D exists in two main dietary forms. D3, or cholecalciferol, forms in the skin with sunlight and appears in some animal-based foods and supplements.
The test is done with 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.
Who might consider this test?
- Look into a vitamin D marker when they are exploring bone and muscle health
- Aches without an obvious cause
- Some prefer a version that breaks out the D2 and D3 forms
Test details
| Quest code | 92888 |
|---|---|
| Methodology | Chromatography/Mass Spectrometry |
| Sample type | 0.5 mL serum |
| Patient preparation | Fast before your blood draw if you can; water is fine. |
| Collection | Quest patient service center |
Related tests and panels
Measures 25-hydroxy vitamin D in blood, reported as separate D2 and D3 forms…
Quest resources
Additional details
What this test looks at
The test measures 25-hydroxyvitamin D, the form that best represents how much vitamin D is available from all sources combined. What sets this version apart is that it reports the D2 and D3 forms on their own as well as together, so the breakdown is visible rather than blended into a single number.
That detail can matter because the two forms tend to trace back to different origins — D3 to sunlight and animal-based sources, D2 more often to plant-based sources and specific supplements. A clinician may find the split useful, but the individual forms still need to be interpreted together and in context, not read in isolation.
How the D2 and D3 breakdown is used
Reporting the forms separately can help a clinician see the fingerprint of what a person is taking or eating. For example, a noticeable D2 contribution may point toward a particular kind of supplement, while D3 reflects sunlight and animal-based sources. This is descriptive information rather than a verdict on its own. The clinician weighs the pattern alongside a person's habits, symptoms, and any other markers before drawing conclusions about overall status.
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 QuestAssureD 25-Hydroxy test measure?
It measures 25-hydroxyvitamin D, the circulating form used to look at vitamin D status, and reports the D2 and D3 forms separately as well as together.
What is the difference between vitamin D2 and D3?
D3 (cholecalciferol) forms in the skin with sunlight and appears in some animal-based foods and supplements, while D2 (ergocalciferol) comes largely from plant-based sources and certain supplements. Both are converted into 25-hydroxyvitamin D.
Why report the D2 and D3 forms separately?
Seeing the forms on their own can help a clinician understand where a person's vitamin D is coming from, which is useful when someone is taking a supplement and the source contribution matters.
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.
Can I interpret the D2 and D3 breakdown myself?
A clinician is best placed to read the breakdown alongside a person's habits, symptoms, 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 QuestAssureD 25-OH test cost?
The cash price at Celio Health is $245. 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.
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.