Vitamins and nutrition . Patient guide
Vitamin D3 Blood Test
What is Vitamin D3
Vitamin D3 (cholecalciferol) is the form of vitamin D your skin makes from sunlight and the form used in most supplements. This is a specialised measurement of that form; the standard test of overall vitamin D status is 25-OH vitamin D.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in nmol/L. Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Interpretation | assay-specific | read against the 25-OH vitamin D status thresholds below and with clinical advice |
| 25-OH vitamin D: deficient | under 25 | nmol/L |
| 25-OH vitamin D: insufficient | 25 to 50 | nmol/L |
| 25-OH vitamin D: sufficient | over 50 | nmol/L |
What it is
The vitamin D your body uses comes mainly as D3 (cholecalciferol), which is converted in the liver to 25-hydroxyvitamin D, the marker labs normally measure to judge status. A direct D3 measurement is a more specialised request, so it is interpreted carefully and always alongside the standard 25-OH test.
Why a clinician would order it
A direct vitamin D3 measurement is occasionally requested to look specifically at the cholecalciferol form, for example when investigating supplementation or absorption. For assessing whether you are deficient or sufficient, the 25-OH vitamin D test is the standard and is what most people should have.
If your level is outside the range
Symptoms of low Vitamin D3
- Fatigue
- Bone or muscle aches
- Low mood
- Frequent infections
- Hair shedding (with prolonged deficiency)
What low can indicate. Low sun exposure (especially in UK winters), darker skin, covering up, older age, malabsorption, or simply low intake.
Symptoms of high Vitamin D3
- Very high levels (usually from over-supplementation) can raise blood calcium, causing nausea, thirst and kidney problems
What high can indicate. High-dose supplementation. Genuine vitamin D toxicity is rare but important because it raises calcium.
Testing tips
For most people the standard 25-OH vitamin D test is the right one; this direct D3 test is a more specialised request best chosen with clinical guidance. See the main vitamin D page for status thresholds and supplementation advice.
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.
Common questions about Vitamin D3
What is a normal Vitamin D3 range?
Interpretation: assay-specific (read against the 25-OH vitamin D status thresholds below and with clinical advice). 25-OH vitamin D: deficient: under 25 (nmol/L). 25-OH vitamin D: insufficient: 25 to 50 (nmol/L). 25-OH vitamin D: sufficient: over 50 (nmol/L). Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low Vitamin D3 result mean?
Low sun exposure (especially in UK winters), darker skin, covering up, older age, malabsorption, or simply low intake.
What does a high Vitamin D3 result mean?
High-dose supplementation. Genuine vitamin D toxicity is rare but important because it raises calcium.
Do I need to fast or prepare for the Vitamin D3 blood test?
For most people the standard 25-OH vitamin D test is the right one; this direct D3 test is a more specialised request best chosen with clinical guidance. See the main vitamin D page for status thresholds and supplementation advice.
Can I order a Vitamin D3 blood test privately in London?
Yes. WMG Health offers Vitamin D3 as part of bespoke panels and several pre-built panels at our 134 Harley Street clinic. Results are clinician-reviewed by a GMC-registered doctor within 4 hours for the most common assays. All panels are custom-built around your specific question; bookings via /contact/ or 020 3239 3378.