Quick Facts
- Sample: Frozen serum (0.25–0.5 mL)
- Fasting: Not required
- Turn-around: 6-10 business days. May take longer based on weather, holiday, or lab delays.
Benefits
- Accurate vitamin D status assessment using frozen samples that preserve analyte stability during transport
- Distinguish vitamin D2 and D3 forms with advanced LC-MS/MS or immunoassay technology for precision
- Convenient online ordering with confidential results and optional physician consultation available
- Guide personalized supplementation to prevent deficiency-related bone, immune, and metabolic disorders
- Monitor therapy effectiveness if you're already taking vitamin D supplements or undergoing treatment
Who Is This Test For?
- Individuals with symptoms like fatigue, bone pain, muscle weakness, or frequent infections
- Those with limited sun exposure or living in northern climates with reduced sunlight
- People following diets low in vitamin D-rich foods (fatty fish, fortified dairy)
- Adults with malabsorption conditions such as celiac disease, Crohn's disease, or gastric bypass
- Pregnant or breastfeeding women monitoring nutritional status for maternal and infant health
- Older adults (65+) at higher risk for deficiency and bone loss
- Anyone taking vitamin D supplements who needs to verify current levels
How It Works – Just 3 Steps
- Order online – Purchase your test through Walk-In Lab's secure website without a doctor's visit
- Visit a lab – Get your blood drawn at a local partner facility; sample is frozen to preserve integrity
- Receive results – Access your confidential report online within 6–10 business days.
FAQ
What does this test measure? It quantifies total 25-hydroxyvitamin D (25(OH)D), the primary circulating form reflecting vitamin D from sun exposure, food, and supplements (Mayo Clinic 2025).
Why is the sample frozen? Freezing preserves vitamin D stability during transport, ensuring reliable and accurate test results even with shipping delays (NIH 2025).
Do I need to fast before this test? No, fasting is generally not required, but follow any specific instructions provided by your lab.
How long until I get my results? Turnaround time ranges from 6–10 days depending on the laboratory and testing method used.
Can I take this test if I'm on supplements? Yes, this test is ideal for monitoring whether your current supplementation regimen is achieving optimal vitamin D levels.
What if my results show deficiency? Your healthcare provider can recommend appropriate vitamin D supplementation, dietary changes, or increased safe sun exposure to restore healthy levels.
More Details
What is the purpose of this test?
The Vitamin D-25 Hydroxy Frozen Blood Test measures total 25-hydroxyvitamin D in your blood, the most reliable indicator of vitamin D status. It reflects vitamin D produced by your skin from sunlight plus amounts obtained from dietary sources and supplements. This test uses frozen serum samples analyzed by chemiluminescent immunoassay or liquid chromatography-tandem mass spectrometry (LC-MS/MS) for high precision (AACE 2024). The test distinguishes between vitamin D2 (from plant sources and fortified foods) and D3 (from sun exposure and animal sources), providing a comprehensive assessment of your total vitamin D supply. Vitamin D is essential for calcium absorption, bone strength, immune function, and muscle health.
Who would benefit from this test?
This test is valuable for individuals at risk of vitamin D deficiency or those monitoring their vitamin D therapy. Older adults face higher deficiency risk due to reduced skin synthesis and dietary intake. People with limited sun exposure—whether from indoor lifestyles, living in northern latitudes, or consistently using sunscreen—may have inadequate levels. Those with malabsorption disorders like celiac disease, inflammatory bowel disease, or gastric bypass surgery often cannot absorb sufficient vitamin D from food. Pregnant and breastfeeding women benefit from monitoring to support fetal development and infant health. Anyone experiencing symptoms like bone pain, fatigue, muscle weakness, or frequent infections should consider testing. Approximately 40% of U.S. adults have inadequate vitamin D levels below 30 ng/mL (NIH 2025).
When should I order the Vitamin D-25 Hydroxy Frozen Blood Test?
Consider ordering this test if you experience symptoms suggesting vitamin D deficiency, including persistent fatigue despite adequate rest, frequent bone or back pain, recurring colds or flu, depressed mood, difficulty sleeping, hair loss, poor wound healing, or muscle cramps and weakness. You should also test before starting vitamin D supplementation to establish your baseline level, during therapy to monitor effectiveness, or if you have chronic conditions affecting vitamin D metabolism like kidney disease, liver disease, or autoimmune disorders. Testing is advisable if you take medications that interfere with vitamin D absorption, such as certain anticonvulsants or corticosteroids. Vitamin D insufficiency elevates risks for osteoporosis, autoimmune disorders, and increased susceptibility to infections (CDC 2025).
How do I interpret the results?
Your results report your total 25-hydroxyvitamin D concentration in nanograms per milliliter (ng/mL). Clinical interpretation should be discussed with your healthcare provider, who will consider your individual health context:
< 20 ng/mL
- Meaning: Deficiency
- Typical action: Supplementation required; investigate underlying causes
20–30 ng/mL
- Meaning: Insufficiency
- Typical action: Increase vitamin D intake through diet, supplements, or sun exposure
30–50 ng/mL
- Meaning: Sufficiency
- Typical action: Maintain current vitamin D intake; optimal for most individuals
> 50 ng/mL
- Meaning: High normal to excess
- Typical action: Reduce supplementation if taking high doses; monitor for toxicity
LC-MS/MS testing increases assay precision over standard immunoassays, improving clinical decision-making and reducing misclassification of vitamin D status (AACE 2024).
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 fasting is required for this test, making it convenient to schedule at any time. You can take your regular medications and supplements as prescribed. The blood sample must be collected as serum using proper collection tubes, then frozen immediately or kept frozen during transport to the laboratory to preserve vitamin D stability. Separate serum promptly after collection to avoid analyte degradation. Follow any specific instructions provided by your testing facility regarding sample handling. Inform your healthcare provider about all medications, supplements, and health conditions, as these may affect vitamin D levels or interpretation.
How often should I get tested?
Testing frequency depends on your individual circumstances, vitamin D status, and treatment goals. Discuss the appropriate schedule with your healthcare provider:
- Initial screening or new symptoms: once, then follow provider guidance
- Confirmed deficiency under treatment: retest after 3–4 months of supplementation
- Monitoring maintenance therapy: every 6–12 months
- High-risk conditions (malabsorption, chronic disease): every 3–6 months
- Optimal levels without risk factors: annually or as symptoms develop
Why early detection matters
Early identification of vitamin D deficiency allows timely intervention before serious health consequences develop. Prolonged deficiency weakens bones, increasing fracture risk and potentially causing osteomalacia in adults or rickets in children. Low vitamin D compromises immune function, making you more susceptible to infections and potentially worsening autoimmune conditions. Deficiency contributes to muscle weakness, increasing fall risk, particularly in older adults. Emerging research links inadequate vitamin D to cardiovascular disease, certain cancers, and metabolic disorders, though more studies are needed. Correcting deficiency through supplementation, dietary changes, and safe sun exposure is straightforward and effective when guided by testing. Regular monitoring ensures you maintain optimal levels for bone health, immune support, and overall wellbeing.
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 #1 Baseline Blood Test Panel – Checks your levels of Vitamin B12, Vitamin K1, and Vitamin D to help identify any deficiencies that may affect your energy, bone strength, and overall health.
