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Understanding This Test: A Patient Guide to What It Is and Why Your Doctor May Order It

Published: August 9, 2026Updated: August 10, 2026

A blood test that measures the level of 25-hydroxyvitamin D in your blood to assess your vitamin D status.

Quick summary

{"Measures 25-hydroxyvitamin D (25(OH)D), the major form of vitamin D in blood","Helps diagnose vitamin D deficiency or excess","Results reflect both vitamin D2 (plant-based) and vitamin D3 (animal-based) intake","Typically performed on a blood serum sample","Used to monitor bone health, calcium metabolism, and certain chronic conditions"}

Medically reviewed by WellAlly Editorial TeamLast reviewed August 10, 2026Editorial policy

Key facts at a glance

LOINC
68438-1
Short code
VITD25
Synonyms
25(OH)D3+25(OH)D2 SerPl-sCnc
Category
chemistry
Sample
serum
Container
Serum separator tube (SST/gold top) or plain red top tube
Units
N/A
Ref low
50
Ref high
250
Critical range
25 N/A – 375 N/A
Fasting
false
Population
adult
Sex
all
Age range
≥ 18 years
Method
Chemiluminescence Immunoassay (CLIA) or Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
CPT
82306
SNOMED
368009
Specimen volume
1.0-2.0 mL of serum
Stability
Room temperature: 7 days; Refrigerated (2-8°C): 14 days; Frozen (-20°C or below): 30 days. Protect from light exposure.
Hemolysis max
50
Lipemia max
300
Icterus max
40
TAT
24–72 hours
Order
routine

What is this test and why has my healthcare provider recommended it for me?

The 25-hydroxyvitamin D test measures the amount of 25-hydroxyvitamin D in your blood serum. This test is considered the best indicator of your body's vitamin D status because 25(OH)D is the major form of vitamin D that circulates in the bloodstream and has a relatively long half-life.

Vitamin D exists in two main forms: vitamin D2 (ergocalciferol, from plant sources and supplements) and vitamin D3 (cholecalciferol, from sunlight exposure, animal foods, and supplements). This test measures both forms together to give a total picture of your vitamin D status.

During the test, a healthcare professional will draw a small sample of blood from a vein in your arm. The sample is then sent to a laboratory for analysis. No special preparation is usually required, though your doctor may ask you to fast for a short period.

Reference range

Deficient: <50 nmol/L; Insufficient: 50-74 nmol/L; Sufficient: 75-250 nmol/L; Toxicity: >250 nmol/LN/A

Specimen: serum

No special preparation required. Fasting is not mandatory but may be recommended depending on laboratory protocol. Inform the laboratory of any vitamin D supplements or medications that may affect results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Vitamin D is essential for maintaining healthy bones and teeth, supporting the immune system, and regulating calcium and phosphorus absorption. Adequate vitamin D levels help prevent rickets in children and osteomalacia or osteoporosis in adults.

Low 25-hydroxyvitamin D levels may indicate vitamin D deficiency, which can result from limited sun exposure, inadequate dietary intake, certain malabsorption disorders (such as Crohn's disease or celiac disease), kidney or liver disease, or certain medications. Symptoms of deficiency may include bone pain, muscle weakness, fatigue, and increased risk of fractures.

Abnormally high levels of vitamin D (vitamin D toxicity) can occur from excessive supplementation and may lead to hypercalcemia, causing symptoms such as nausea, vomiting, weakness, and kidney problems.

This test is commonly ordered for patients with bone disorders, chronic kidney disease, certain autoimmune conditions, and those at risk for vitamin D deficiency, including older adults, people with limited sun exposure, and individuals with darker skin.

Frequently asked questions

What do the results mean?
Results are typically reported in ng/mL or nmol/L. Generally, levels below 20 ng/mL (50 nmol/L) indicate vitamin D deficiency, 20-30 ng/mL (50-75 nmol/L) may indicate insufficiency, and 30-100 ng/mL (75-250 nmol/L) is considered sufficient. However, target ranges may vary by laboratory and individual health factors. Your healthcare provider will interpret your results in context.
How often should I have this test?
The frequency of testing depends on your individual risk factors and health conditions. Your doctor may recommend initial testing to establish your baseline vitamin D status, followed by repeat testing after 3-6 months of supplementation or lifestyle changes to monitor effectiveness.
Do I need to fast before the test?
Fasting is usually not required for this test. However, always follow your healthcare provider's specific instructions. Inform your doctor about any vitamin D supplements or medications you are taking, as these may affect your results.
What can I do to improve my vitamin D levels?
You can increase vitamin D levels through safe sun exposure (typically 10-30 minutes several times per week), consuming vitamin D-rich foods such as fatty fish, egg yolks, and fortified dairy or plant-based products, or taking vitamin D supplements as recommended by your healthcare provider.
  1. 1
    MedlinePlus - Vitamin D TestSource
  2. 2
    Mayo Clinic - Vitamin DSource
  3. 3
    Lab Tests Online - 25-Hydroxy Vitamin D TestSource

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.

Medical Disclaimer

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