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Vitamin D 25-Hydroxy (25(OH)D) Serum Level

Published: August 9, 2026Updated: August 17, 2026

This test measures the level of vitamin D in your blood, specifically the 25-hydroxy form, which is the active form your body uses to regulate calcium and bone health.

Quick summary

Vitamin D levels help assess your risk of deficiency and support bone and immune health.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
43134-6
Short code
Vit D25+D1,25 OH+D1,25 Pnl SerPl-mCnc
Synonyms
Vit D25+D1,25 OH+D1,25 Pnl SerPl-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
30
Ref high
100
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Matters

Vitamin D is essential for maintaining strong bones, supporting muscle function, and boosting the immune system. Low levels can lead to health issues like bone pain, fatigue, or increased susceptibility to infections. Your doctor may recommend this test if you have symptoms of deficiency or if you’re at higher risk due to lifestyle or medical conditions.

What to Expect Before the Test

No special preparation is needed for this test. You’ll have a small needle inserted into your arm to draw blood. It usually takes a few minutes. If you’re on vitamin D supplements, your doctor may advise stopping them for a few days before testing to get an accurate result.

What the Results Mean

Results are typically reported in nanograms per deciliter (ng/dL). While reference ranges can vary slightly by lab, levels below 20 ng/dL are considered deficient, between 20–30 ng/dL are insufficient, and 30 ng/dL or higher are generally considered adequate.

Common Causes of Low or High Levels

Low vitamin D levels may be due to limited sun exposure, certain medications, digestive issues, or obesity. High levels can result from overuse of supplements or certain medical conditions. Your doctor may recommend lifestyle changes, supplements, or further testing if needed.

Reference range

NCBI: Vitamin D 30-100 ng/mL (sufficient)N/A

Specimen: serum

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Vitamin D Blood Test

Frequently asked questions

What Might This Test Be Used For?
This test is often used to diagnose vitamin D deficiency, which can lead to weakened bones (osteoporosis), muscle weakness, or increased risk of certain illnesses. It may also be checked during pregnancy, in people with chronic illnesses, or those who spend little time outdoors.
How Often Should I Get This Test?
Your doctor will determine how often you need this test based on your health status, age, and risk factors. Typically, adults may get it every 1–2 years if levels are normal, but more frequent testing may be recommended if you have conditions like kidney disease or are taking certain medications.
What If My Results Are Abnormal?
If your results show low vitamin D levels, your doctor may suggest dietary changes, increased sun exposure, or supplements to help restore balance. If levels are high, they may investigate underlying causes like over-supplementation or certain medical conditions before recommending adjustments.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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 17, 2026. · Read our editorial policy