Understanding Your Blood Test: What It Is, Why It Is Done, and What the Results Mean
A blood test that measures the level of 25-hydroxyvitamin D (calcidiol) in your blood to evaluate vitamin D status.
{"This test measures your body's stored vitamin D (both D2 and D3 forms)","Low levels may indicate vitamin D deficiency affecting bone health","The test requires a simple blood sample, typically from a vein in your arm","Results help doctors diagnose bone disorders and assess calcium absorption issues","No special fasting is usually required before this test"}
Key facts at a glance
- LOINC
- 83070-3
- Short code
- 25-OH Vit D
- Synonyms
- 25(OH)D3+25(OH)D2 SerPl IA-mCnc
- Category
- chemistry
- Sample
- serum
- Container
- SST (Serum Separator Tube) or plain red top tube
- 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
- Immunoassay
- CPT
- 82306
- SNOMED
- 365757006
- Specimen volume
- 1.0 mL minimum, 2.0 mL preferred
- Stability
- Room temperature: 24 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days
- Hemolysis max
- 400
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 24–72 hours
- Order
- routine
What is this test and what does it check?
The 25-hydroxyvitamin D test measures the amount of 25-hydroxyvitamin D in your blood. This form of vitamin D is produced when your body processes vitamin D from sunlight, food, or supplements. It is the best indicator of your overall vitamin D status because it reflects both vitamin D2 (ergocalciferol, from plant sources and supplements) and vitamin D3 (cholecalciferol, from sunlight and animal sources). The test uses an immunoassay method to detect and measure these compounds in your serum (blood) sample.
Why might I need this test?
Your healthcare provider may order this test if you have symptoms of vitamin D deficiency, such as bone pain, muscle weakness, or fatigue. It is also used to diagnose and monitor conditions like rickets, osteomalacia, and osteoporosis. The test helps evaluate how well your body absorbs calcium, which is essential for strong bones and teeth. Additionally, it may be ordered if you have kidney disease or malabsorption disorders, as these conditions can affect vitamin D metabolism.
How is the test performed and what can I expect during the procedure?
A healthcare professional will draw a small sample of blood from a vein in your arm using a needle. The blood is collected into a tube and sent to a laboratory for analysis. The procedure only takes a few minutes and is generally well-tolerated. You typically do not need to fast before this test, but follow any specific instructions your healthcare provider gives you.
Your results are compared with a reference range printed on your report. A value outside this range does not always mean you have a health problem, and normal values do not always rule one out. Your healthcare provider will review the findings along with your symptoms, medical history, and other tests to explain what they mean and whether any follow-up testing or treatment is needed.
Results are typically reported in nanograms per milliliter (ng/mL) or nmol/L. Generally, a level of 20 ng/mL (50 nmol/L) or higher is considered adequate for most people. Levels below 20 ng/mL may indicate vitamin D deficiency, while levels below 10 ng/mL indicate severe deficiency. Levels above 150 ng/mL may suggest vitamin D toxicity. Your doctor will interpret your results based on your overall health, symptoms, and other factors.
Reference range
Sufficient: 30-100 ng/mL (75-250 nmol/L); Insufficient: 20-29 ng/mL (50-74 nmol/L); Deficient: <20 ng/mL (<50 nmol/L); Toxicity: >150 ng/mL (>375 nmol/L)N/A
No fasting required. Patient may take medications as prescribed. Specimen can be collected at any time of day. Avoid excessive handling of specimen tube to prevent hemolysis.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Vitamin D is essential for calcium absorption and maintaining healthy bones and teeth. Low 25-hydroxyvitamin D levels can lead to rickets in children and osteomalacia or osteoporosis in adults. This test helps diagnose the cause of abnormal calcium levels, bone deformities, bone pain, and muscle weakness. It is also important for evaluating patients with chronic kidney disease, as kidney function affects vitamin D activation. Additionally, adequate vitamin D levels play a role in immune function, and research suggests associations between vitamin D and various chronic conditions, though more studies are needed.
Frequently asked questions
Do I need to fast before the 25-hydroxyvitamin D test?
What happens if my vitamin D levels are too low?
Can I take vitamin D supplements before the test?
How often should I have my vitamin D levels checked?
What foods contain vitamin D?
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