Understanding Your Laboratory Test: A Patient's Guide to What It Is, How It Works, and How to Prepare
This test measures the levels of vitamin D (both D2 and D3 forms) in your blood using a small sample from a finger prick.
{"Measures vitamin D levels in capillary blood from a finger prick","Checks for vitamin D deficiency which affects bone health and calcium absorption","Results help doctors diagnose and monitor bone and mineral disorders","Both vitamin D2 (plant-based) and D3 (sunlight-derived) forms are measured","Normal range is typically 30-100 ng/mL, but may vary by laboratory"}
Key facts at a glance
- LOINC
- 95595-5
- Short code
- 25-OH Vit D Capillary
- Synonyms
- 25(OH)D3+25(OH)D2 BldC-mCnc
- Category
- chemistry
- Sample
- whole-blood
- Container
- Capillary blood collection tube (EDTA or heparinized microcontainer)
- Units
- N/A
- Ref low
- 30
- Ref high
- 100
- Critical range
- 10 N/A – 150 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- Liquid chromatography-tandem mass spectrometry (LC-MS/MS) or Chemiluminescence Immunoassay (CLIA)
- CPT
- 82306
- SNOMED
- 312073009
- Specimen volume
- 50-100 μL (0.05-0.1 mL) of capillary whole blood
- Stability
- Room temperature: 24-48 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C): 30 days. Protect from light exposure.
- Hemolysis max
- 50
- Lipemia max
- 100
- Icterus max
- 20
- TAT
- 24–72 hours
- Order
- routine
What is this test and what does it measure?
The 25-Hydroxyvitamin D test measures the amount of 25-hydroxyvitamin D in your blood. This is the major form of vitamin D that circulates in the body and is considered the best indicator of your vitamin D status. The test measures two forms: vitamin D2 (ergocalciferol, from plant sources and supplements) and vitamin D3 (cholecalciferol, from sunlight exposure and animal sources).
How is this test performed and what can I expect during the procedure?
A healthcare professional will clean your finger with an antiseptic wipe and use a small lancet to prick the finger. A few drops of blood will be collected into a small container or onto a special test card. The sample is then sent to a laboratory for analysis. This capillary blood test is quick and requires only a tiny amount of blood.
Why is this test important for my health and what can the results tell my doctor?
Vitamin D is essential for maintaining healthy bones and teeth because it helps the body absorb calcium from food. Without enough vitamin D, bones can become thin, brittle, or misshapen. This test helps doctors diagnose vitamin D deficiency, which can lead to conditions like rickets in children and osteomalacia or osteoporosis in adults.
How should I prepare for this test, including any steps to take before my appointment?
No special preparation is usually required for this test. You can eat and drink normally before the test. However, inform your doctor about any medications or supplements you are taking, as certain medications can affect vitamin D levels. Fasting is not required for this test.
Reference range
Sufficient: 30-100 ng/mL (75-250 nmol/L); Insufficient: 20-29 ng/mL (50-75 nmol/L); Deficient: <20 ng/mL (<50 nmol/L)N/A
No fasting required. Patient may eat and drink normally before sample collection. Inform about any vitamin D supplements or medications that may affect results.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Vitamin D deficiency is common, especially in people with limited sun exposure, darker skin, older adults, and those with certain medical conditions affecting fat absorption. Low vitamin D levels can cause bone pain, muscle weakness, and increase the risk of fractures. In children, severe deficiency can lead to rickets. The test is also used to monitor vitamin D levels in patients with kidney disease, as the kidneys play a role in converting vitamin D to its active form.
Interpretation of results: Generally, levels below 20 ng/mL are considered deficient, 20-29 ng/mL are insufficient, and 30-100 ng/mL are sufficient. However, target ranges may vary slightly between laboratories. Your doctor will interpret your results based on your overall health and risk factors.
Frequently asked questions
What happens if my vitamin D level is low?
Can I take vitamin D supplements before the test?
How often should I have this test?
Does this test require fasting?
What is the difference between vitamin D2 and D3?
Sources
- 1
- 2Mayo Clinic - Vitamin DSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 10, 2026. · Read our editorial policy