Understanding Your Lab Test: What It Is, Why It Is Done, and How the Procedure Works
This blood test measures different forms of vitamin D (D2 and D3) and their byproducts to evaluate your vitamin D status and how your body processes this important nutrient.
{"Measures 25-hydroxyvitamin D2 and D3 (main storage forms)","Also measures 24,25-dihydroxyvitamin D (breakdown product)","Helps diagnose vitamin D deficiency or excess","The ratio can reveal how well your body is processing vitamin D","Used to monitor vitamin D supplementation effectiveness"}
Key facts at a glance
- LOINC
- 94673-1
- Short code
- VitD3D2-24,25DH-VitDRatio
- Synonyms
- 25(OH)D3+25(OH)D2/24,25(OH)2 VitD SerPl
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST/gel tube) or plain red top tube. Avoid hemolyzed specimens.
- Units
- N/A
- Ref low
- 5
- Ref high
- 25
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
- CPT
- 82306 (25-Hydroxyvitamin D), 82552 (24,25-Dihydroxyvitamin D)
- SNOMED
- 371501006 (25-Hydroxyvitamin D measurement), 371502004 (24,25-Dihydroxyvitamin D measurement)
- Specimen volume
- 1.0-2.0 mL serum minimum
- Stability
- Room temperature: 24-48 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30-90 days. Protect from light exposure.
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 48–168 hours
- Order
- routine
This test is a laboratory analysis that gives your health care team important information about how your body is working. It can detect changes that may not cause noticeable symptoms, and the results are compared with standard reference ranges to help guide your care.
This test measures the levels of different vitamin D forms in your blood. Vitamin D exists in two main forms: D2 (ergocalciferol) from plant sources and supplements, and D3 (cholecalciferol) from sunlight exposure and animal sources. Your liver converts both forms into 25-hydroxyvitamin D, which is the major form stored in your body. The test also measures 24,25-dihydroxyvitamin D, a byproduct created when your body breaks down vitamin D. By looking at the ratio of these substances, doctors can understand how well your body is absorbing and using vitamin D.
Your doctor may order this test to screen for a health condition before symptoms appear, to help confirm or rule out a diagnosis when you are not feeling well, to monitor an ongoing condition, or to check how well a treatment is working during a routine follow-up.
This test helps healthcare providers assess your overall vitamin D status. It is commonly ordered when someone has symptoms of vitamin D deficiency, such as bone pain, muscle weakness, or frequent fractures. It is also useful for monitoring people taking vitamin D supplements to ensure proper dosing, and for patients with conditions that affect vitamin D absorption or metabolism, such as kidney disease, liver disease, or digestive disorders.
The test is usually done by collecting a small sample, most often a blood draw from a vein in your arm, and the procedure typically takes only a few minutes. The sample is then sent to a laboratory, and your provider will contact you to discuss the results once they are ready.
A healthcare professional will draw a small blood sample from a vein in your arm. This sample is then sent to a laboratory for analysis. You do not need to fast before this test, but you should inform your doctor about any supplements or medications you are taking, as they may affect the results.
Reference range
The 25-Hydroxyvitamin D3 to 24,25-Dihydroxyvitamin D3 ratio (3-epi-25-hydroxyvitamin D3 excluded) reference range is typically 5-25 in healthy adults. The 25-Hydroxyvitamin D2 contribution to total 25-Hydroxyvitamin D is typically <20% in patients without D2 supplementation. Interpretation should be correlated with clinical findings and 25-Hydroxyvitamin D total levels.N/A
No special preparation required. Patient does not need to fast. Maintain standard hydration status. Avoid vitamin D supplements within 24 hours of collection if clinically appropriate, but follow ordering physician instructions.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Low levels of 25-hydroxyvitamin D may indicate vitamin D deficiency, which can lead to rickets in children and osteomalacia or osteoporosis in adults. High levels may suggest vitamin D toxicity, which can cause nausea, weakness, and kidney problems. The ratio of 25-hydroxyvitamin D to 24,25-dihydroxyvitamin D can help doctors understand if there are issues with vitamin D metabolism, which is particularly important in patients with chronic kidney disease or certain genetic conditions.
Frequently asked questions
How much vitamin D do I need daily?
What are the symptoms of vitamin D deficiency?
Can I get enough vitamin D from sunlight alone?
What foods contain vitamin D?
Sources
- 1Mayo Clinic - Vitamin DSource
- 2
- 3
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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