Medical Laboratory Test: What It Is, How It Is Performed, and What Your Results Mean
A blood test that measures the level of 25-hydroxyvitamin D, the major form of vitamin D in your blood, to check your vitamin D status.
{"This test measures 25-hydroxyvitamin D, the best indicator of your body's vitamin D levels","Low levels may indicate vitamin D deficiency, which can affect bone health and immune function","The test requires a simple blood draw, usually from a vein in your arm","Results help doctors diagnose deficiency and monitor treatment effectiveness","No special preparation is typically needed, but follow your doctor's instructions"}
Key facts at a glance
- LOINC
- 14635-7
- Short code
- 25-OH Vitamin D
- Synonyms
- 25(OH)D3 SerPl-sCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum Separator Tube (SST) or plain red top tube
- Units
- N/A
- Ref low
- 75
- Ref high
- 250
- Critical range
- 25 N/A – 375 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- Chemiluminescence Immunoassay (CLIA)
- CPT
- 82306
- SNOMED
- 371441009
- Specimen volume
- 1.0-2.0 mL serum minimum
- Stability
- Room temperature: 24 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 40
- TAT
- 24–72 hours
- Order
- routine
This test is a laboratory analysis that helps your doctor evaluate your overall health and screen for, diagnose, or monitor certain medical conditions. It measures specific substances or markers in a sample from your body, and the findings guide decisions about your care, any follow-up testing, and the treatment that may be right for you.
The 25-hydroxyvitamin D test measures the amount of 25-hydroxyvitamin D in your blood. This is the major circulating form of vitamin D and is considered the most accurate indicator of your overall vitamin D status. Vitamin D is essential for maintaining healthy bones, supporting the immune system, and regulating calcium and phosphate levels in the body.
The test is usually performed in a clinic, hospital, or laboratory. A trained healthcare professional will collect a small sample, often by drawing blood from a vein in your arm or by asking you to provide a urine specimen. The procedure typically takes only a few minutes, causes little discomfort, and you can usually return to your normal activities right afterward.
A healthcare professional will draw a small blood sample 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 typically takes only a few minutes. You may experience slight pain or bruising at the injection site, but serious complications are rare.
Your results show whether the measured values fall within the normal reference range for your age and sex. Values that are higher or lower than expected may point to an infection, a chronic condition, or another issue that needs follow-up, but they do not always mean you are sick. Your doctor will interpret the findings together with your symptoms, medications, and medical history, and explain what they mean for your health.
Vitamin D levels are typically measured in nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L). Generally, levels below 20 ng/mL (50 nmol/L) indicate vitamin D deficiency, while levels between 20-30 ng/mL (50-75 nmol/L) may indicate insufficiency. Optimal levels are usually considered to be above 30 ng/mL (75 nmol/L). However, target ranges may vary based on individual health factors and your doctor's recommendations.
Reference range
Deficient: <50 nmol/L; Insufficient: 50-75 nmol/L; Sufficient: 75-250 nmol/L; Optimal: 100-150 nmol/L; Toxicity: >375 nmol/LN/A
No fasting required. Collect at any time of day. Avoid prolonged exposure to sunlight immediately before collection. Inform physician of any vitamin D supplements or medications.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Vitamin D deficiency is common and can lead to bone diseases such as osteomalacia (soft bones) in adults and rickets in children. Low vitamin D levels have also been associated with increased risk of fractures, muscle weakness, fatigue, depression, and impaired immune function. Certain groups are at higher risk, including older adults, people with limited sun exposure, individuals with darker skin, those with malabsorption disorders, and people who are obese. Your doctor may order this test if you have symptoms of deficiency, have bone disease, or are at risk for vitamin D insufficiency.
Elevated vitamin D levels (usually above 150 ng/mL or 375 nmol/L) can indicate vitamin D toxicity, which is often caused by excessive supplementation. This can lead to hypercalcemia (high blood calcium), causing symptoms like nausea, vomiting, weakness, and kidney problems. The 25-hydroxyvitamin D test helps doctors diagnose both deficiency and excess, allowing them to recommend appropriate treatment including dietary changes, supplements, or lifestyle modifications.
Frequently asked questions
Do I need to fast before this test?
How often should I have my vitamin D levels checked?
Can I get enough vitamin D from sunlight alone?
What foods contain vitamin D?
Will I need to take supplements if my levels are low?
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