Quick Facts
- Sample: Blood (serum)
- Fasting: Preferred but not mandatory
- Turn-around: 4-10 business days. May take longer based on weather, holiday, or lab delays.
Benefits
- Gold-standard precision: LC-MS/MS technology measures D2 and D3 separately for accurate results (Mayo Clinic 2025)
- Empowers your health decisions: Know your exact vitamin D status to optimize supplementation
- Convenient and confidential: Order online, get tested locally, receive secure results quickly
- Supports bone and immune health: Identify deficiencies before they lead to fractures or illness
- Guides personalized treatment: Track your response to vitamin D therapy over time
Who Is This Test For?
- People with limited sun exposure or those living in northern climates
- Individuals experiencing unexplained bone pain, muscle weakness, or frequent infections
- Those with darker skin tones who may have reduced vitamin D synthesis
- Anyone with malabsorption disorders like celiac disease or Crohn's disease
- Patients taking medications that affect vitamin D metabolism (anticonvulsants, glucocorticoids)
- Individuals on vitamin D supplementation who want to monitor their levels
- People diagnosed with osteoporosis, osteopenia, or metabolic bone disorders
- Those with parathyroid or calcium metabolism concerns
How It Works – Just 3 Steps
- Order online: Purchase your test kit through our secure platform—no doctor's visit required
- Visit a lab near you: Get your blood drawn at a convenient local collection site
- Receive your results: Access your confidential results online within 4–10 business days.
FAQ
What does this test measure? This test measures total 25-hydroxyvitamin D, including both D2 (from plants and fortified foods) and D3 (from sunlight and animal sources), which reflects your body's vitamin D stores (Mayo Clinic 2025).
Why is LC-MS/MS better than other vitamin D tests? LC-MS/MS provides superior precision and fewer false results compared to standard immunoassays, and it can differentiate between D2 and D3 forms for detailed analysis (AACE 2024).
Do I need to fast before this test? Fasting for 8–12 hours is preferred for standardization but not mandatory. Consult your healthcare provider for specific instructions.
How long until I get my results? Results are typically available within 4–10 business days after your sample reaches the laboratory.
What's considered a normal vitamin D level? Levels above 30 ng/mL are generally sufficient for bone and overall health, while 20–30 ng/mL indicates insufficiency and below 20 ng/mL indicates deficiency.
Can I use this test to monitor my vitamin D supplements? Yes, this test is excellent for tracking your response to supplementation and ensuring you're reaching optimal levels.
More Details
What is the purpose of this test?
The Vitamin D 25-Hydroxy (D2+D3 Fractionated) Blood Test measures the total circulating levels of 25-hydroxyvitamin D in your blood, the most reliable indicator of your body's vitamin D stores (NIH 2025). Since 25-hydroxyvitamin D has a long half-life and is the major circulating metabolite, it provides the best assessment of vitamin D sufficiency. This test uses highly sensitive LC-MS/MS technology with deuterated internal standards to separately quantify both vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), giving you a detailed and accurate profile of your vitamin D status.
Vitamin D plays a crucial role in calcium absorption, bone mineralization, immune function, and cellular growth regulation. Deficiencies can lead to rickets in children, osteomalacia in adults, increased fracture risk, and potentially weakened immune response (CDC 2025). By measuring both forms individually, this test helps identify whether you're getting adequate vitamin D from sun exposure, diet, or supplements, enabling you and your healthcare provider to make informed decisions about treatment.
What biomarkers are measured in this test?
- Vitamin D2 (ergocalciferol): Obtained primarily from plant sources and fortified foods
- Vitamin D3 (cholecalciferol): Synthesized by skin from sunlight and found in animal-based foods
- Total 25-Hydroxyvitamin D: The sum of D2 and D3 representing overall vitamin D status
Who would benefit from this test?
This test is particularly valuable for individuals at risk of vitamin D deficiency or those managing conditions affected by vitamin D status. About 40% of U.S. adults have insufficient vitamin D levels below 30 ng/mL (NIH 2025), making routine screening important for many people.
You may benefit from this test if you have limited sun exposure, live in northern latitudes, work indoors, or consistently use sunscreen. People with darker skin tones require more sun exposure to produce adequate vitamin D and are at higher risk of deficiency. Those with malabsorption disorders such as celiac disease, Crohn's disease, or cystic fibrosis may not absorb vitamin D efficiently from food.
Additionally, this test is recommended for individuals with bone disorders including osteoporosis, osteopenia, or a history of fractures. Patients on medications that interfere with vitamin D metabolism—such as anticonvulsants, glucocorticoids, or certain weight-loss drugs—should monitor their levels regularly. Anyone currently taking vitamin D supplements can use this test to ensure they're achieving optimal levels without risking toxicity.
When should I order this test?
Consider ordering this test if you experience symptoms that may indicate vitamin D deficiency, including persistent bone pain or tenderness, muscle weakness or cramps, unexplained fatigue, frequent infections, depression, or slow wound healing. These symptoms can significantly impact your quality of life and may improve with appropriate vitamin D supplementation.
Testing is also appropriate before starting vitamin D supplementation to establish your baseline level, or during supplementation to verify you're reaching target levels. If you have unexplained hypocalcemia, elevated parathyroid hormone, or metabolic bone disease, this test helps identify whether vitamin D deficiency is a contributing factor.
Healthcare providers may order this test as part of evaluating bone health concerns, diagnosing the cause of rickets or osteomalacia, or assessing parathyroid and calcium metabolism disorders (Mayo Clinic 2025). Annual or biannual testing may be recommended for individuals with chronic conditions affecting vitamin D status or those living in areas with minimal sunlight during winter months.
How do I interpret the results?
Below 20 ng/mL
- Meaning: Deficiency
- Typical action: Supplementation recommended; investigate underlying causes; retest after 8–12 weeks
20–30 ng/mL
- Meaning: Insufficiency
- Typical action: Increase dietary vitamin D and sun exposure; consider supplementation; monitor regularly
30–50 ng/mL
- Meaning: Sufficient
- Typical action: Maintain current intake; continue healthy lifestyle practices; retest annually
50–100 ng/mL
- Meaning: Optimal for most
- Typical action: Continue current regimen; no changes typically needed
Above 100 ng/mL
- Meaning: Potentially excessive
- Typical action: Reduce supplementation; evaluate for hypercalcemia; consult healthcare provider
Deficiency is linked to increased risk of fractures, infections, and chronic diseases, making early detection crucial for prevention (CDC 2025).
The fractionated results showing D2 and D3 separately can help determine whether your vitamin D comes primarily from supplementation (often D2) or sun exposure and diet (D3). Vitamin D3 is more potent and the preferred form for supplementation. Always consult your healthcare provider to interpret your results in the context of your overall health, symptoms, and risk factors.
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
Fasting for 8–12 hours before your blood draw is preferred for standardization but not mandatory. You may drink water during the fasting period. If you're currently taking vitamin D supplements, continue your normal regimen—stopping supplements before the test would not accurately reflect your typical vitamin D status.
Inform your healthcare provider about all medications and supplements you're taking, particularly those that may affect vitamin D metabolism such as anticonvulsants, corticosteroids, cholestyramine, or orlistat. Timing of your test relative to recent vitamin D supplementation changes is important; allow at least 8–12 weeks after adjusting your supplement dose before retesting to allow levels to stabilize.
Your blood sample will be collected in a standard red-top tube. The laboratory requires approximately 0.25–0.5 mL of serum for analysis. Results are typically available within 4–10 business days after the sample reaches the testing facility.
How often should I get tested?
Testing frequency depends on your individual circumstances, risk factors, and current vitamin D status. Here are general guidelines:
- Initial screening or first-time testing: once, then follow frequency based on results
- Vitamin D deficiency (below 20 ng/mL): retest after 8–12 weeks of supplementation
- Insufficiency being treated (20–30 ng/mL): every 3–6 months until levels stabilize
- Sufficient levels with supplementation: every 6–12 months to ensure maintenance
- High-risk individuals (malabsorption, chronic conditions): every 3–6 months or as directed by physician
- Healthy individuals with adequate sun exposure: annually or every 2 years for monitoring
Your healthcare provider may recommend more frequent testing if you have conditions affecting vitamin D absorption or metabolism, are on medications that interfere with vitamin D, or are adjusting your supplementation regimen. Pregnant and breastfeeding women may also benefit from more regular monitoring to ensure adequate vitamin D for themselves and their babies.
Why early detection matters
Vitamin D deficiency often develops gradually and can go unnoticed for years while silently affecting your health. Early detection through testing allows you to address deficiency before it leads to serious complications such as osteoporosis, fractures, or chronic bone pain. Studies show that vitamin D deficiency is linked to increased risk of falls in older adults, reduced immune function, and potentially higher susceptibility to respiratory infections (NIH 2025).
Children with severe vitamin D deficiency can develop rickets, a condition causing soft, weak bones that may lead to skeletal deformities. In adults, deficiency causes osteomalacia, resulting in bone pain, muscle weakness, and increased fracture risk. These conditions are largely preventable with adequate vitamin D intake and early identification of deficiency.
The LC-MS/MS methodology used in this test provides higher precision and fewer false results compared to older immunoassay methods, improving clinical decision-making and reducing unnecessary treatment or missed diagnoses (AACE 2024). By identifying both D2 and D3 levels separately, you gain insight into whether your vitamin D sources are adequate and can adjust your diet, sun exposure, or supplementation accordingly.
Related tests you may consider
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