Quick Facts
- Sample: Blood (serum)
- Fasting: Not required
- Turn-around: 2-3 business days. May take longer based on weather, holiday or lab delays.
Benefits
- Assess vitamin D status — Identify deficiency before symptoms appear
- Monitor supplementation — Verify your vitamin D therapy is working effectively
- Support bone health — Prevent osteoporosis and fractures with informed action
- Boost immune function — Optimize levels linked to infection resistance
- Convenient access — Order online without a doctor's visit required
Who Is This Test For?
- Individuals experiencing bone pain, muscle weakness, or frequent infections
- Adults over 65 at higher risk for vitamin D deficiency
- People with limited sun exposure or darker skin tones
- Those taking vitamin D supplements who want to monitor levels
- Individuals with conditions affecting fat absorption (Crohn's disease, cystic fibrosis)
- Anyone managing osteoporosis or preparing for bone health therapy
How It Works – Just 3 Steps
- Order online - Select your test and complete checkout in minutes
- Visit a lab - Walk into any of 4,500+ locations nationwide for a quick blood draw
- Get results - Access your results online within 2-3 business days.
FAQ
What does this test measure? It measures serum 25-hydroxyvitamin D, the most reliable indicator of your body's vitamin D stores (Mayo Clinic 2024).
Do I need to fast before this test? No, fasting is typically not required for the Vitamin D 25-Hydroxy test.
How is vitamin D deficiency treated? Treatment usually involves dietary changes, increased sun exposure, and vitamin D supplementation as recommended by your healthcare provider.
Can this test distinguish vitamin D2 from D3? Some advanced assays can differentiate between D2 and D3 forms, providing detailed supplementation insights.
What conditions are linked to low vitamin D? Deficiency increases risk for osteoporosis, certain cancers, autoimmune diseases, and infections (CDC 2025).
How quickly will I receive my results? Most results are available within 2-3 business days after your sample is collected.
More Details
What is the purpose of this test?
The Vitamin D 25-Hydroxy Blood Test evaluates your total 25-hydroxyvitamin D levels, which reflect vitamin D from both sunlight exposure and dietary intake. This is the best marker for assessing vitamin D sufficiency because 25(OH)D is the main circulating form with a relatively long half-life (NIH 2025). The test uses sensitive immunoassay or LC-MS/MS methods to provide accurate quantification, helping you and your healthcare provider make informed decisions about supplementation and lifestyle changes.
Who would benefit from this test?
This test is valuable for anyone at risk of vitamin D deficiency, including elderly individuals, those with limited sun exposure, people with darker skin pigmentation, and individuals who are obese or homebound. It's also beneficial for people with malabsorption conditions such as Crohn's disease or cystic fibrosis, those who have undergone gastric bypass surgery, and individuals already on vitamin D therapy who need monitoring. Approximately 40% of U.S. adults have insufficient vitamin D levels, making proactive testing increasingly important (NIH 2025).
When should I order a Vitamin D 25-Hydroxy Test?
Order this test if you experience symptoms of deficiency such as bone pain, muscle weakness, or frequent infections. It's recommended before starting osteoporosis medication, when beginning or adjusting vitamin D supplementation, or as part of routine health monitoring if you have risk factors. Testing is also appropriate for chronic disease management related to immune function, metabolic conditions, or bone health concerns (American Endocrine Society 2023).
How do I interpret the results?
Below 20 ng/mL
- Meaning: Deficiency
- Typical action: Supplementation recommended; dietary and lifestyle changes
20–30 ng/mL
- Meaning: Insufficiency
- Typical action: Moderate supplementation; increased sun exposure
Above 30 ng/mL
- Meaning: Sufficient
- Typical action: Maintain current vitamin D intake and lifestyle
Above 100 ng/mL
- Meaning: Excess (rare)
- Typical action: Reduce supplementation; medical evaluation advised
Vitamin D insufficiency is linked to increased risks of osteoporosis, certain cancers, autoimmune diseases, and infections (CDC 2025).
Disclaimer: Reference ranges may vary by laboratory. Listed ranges are general guidelines and may differ from those used by the performing lab. Always consult your healthcare provider for interpretation.
Pre-test preparation
No special preparation is typically required for this test. Fasting is not necessary, though you should follow any specific instructions provided by your lab. Inform your healthcare provider about any medications or supplements you're taking, particularly high-dose vitamin D supplements. Continue taking your regular medications unless instructed otherwise. The test requires a simple venous blood draw that takes just minutes.
How often should I get tested?
- Initial screening with risk factors: baseline, then annually
- Starting vitamin D supplementation: retest after 3–4 months
- Monitoring supplementation therapy: every 6–12 months
- Managing chronic conditions: as recommended by your provider
- Healthy adults with no risk factors: every 1–2 years or as needed
Why early detection matters
Identifying vitamin D deficiency early prevents serious complications including osteoporosis, bone fractures, and weakened immune function. Vitamin D plays essential roles beyond bone health—it regulates calcium and phosphorus levels, supports immune system function, and influences tissue growth throughout the body. Early detection through accurate measurement reduces misdiagnosis and guides effective supplementation, improving health outcomes (American Endocrine Society 2023). Without adequate vitamin D, children can develop rickets and adults may experience osteomalacia, characterized by bone weakness and increased fracture risk (Johns Hopkins Medicine 2024).
Related tests you may consider
Parathyroid Hormone (PTH) Intact without Calcium Blood Test- Measures the level of PTH in the blood to help screen for osteoporosis and other underlying health conditions.
Calcium Serum Test - Checks the amount of calcium in your blood to help find problems with your bones, muscles, nerves, or kidneys and make sure your calcium levels stay healthy.
Vitamin D 1,25 Dihydroxy (Calcitriol) Blood Test - Checks the active form of vitamin D in your body, helping to find problems related to bone health and vitamin D levels, especially if you have symptoms like bone pain or muscle weakness.
