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Vitamin D, 25-Hydroxy [Serum]

Published: August 9, 2026Updated: August 16, 2026

This test measures the level of 25-hydroxy vitamin D in your blood, a key marker for vitamin D status.

Quick summary

["Your vitamin D levels help determine if you’re getting enough of this essential nutrient for bone health and other functions."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
3195-5
Short code
Fact V Ag Act/Nor PPP IA
Synonyms
Fact V Ag Act/Nor PPP IA
Category
chemistry
Sample
plasma
Container
Lavender-top (EDTA) or Green-top (Heparin)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ia
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 crucial for maintaining strong bones, supporting immune function, and helping your body absorb calcium. Low levels can lead to conditions like osteoporosis or muscle weakness. This test checks whether your body has enough vitamin D to meet your needs.

What to Expect Before the Test

No special preparation is needed for this blood test. You may be asked to fast for 8–12 hours before your blood draw, but this depends on your healthcare provider’s instructions. Wear comfortable clothing and plan to stay near your lab location for about 15 minutes.

What Happens During the Test

A healthcare professional will insert a small needle into your arm to draw blood. You may feel a slight pinch, but the process usually takes just a few minutes. The blood sample is then sent to a lab for analysis.

What the Results Mean

Results are typically reported as a numerical value (in ng/mL or nmol/L), but your doctor will interpret them based on your health history and symptoms. Low levels may prompt dietary or lifestyle changes, while very high levels could require further evaluation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

25-Hydroxy Vitamin D

Frequently asked questions

What are the normal reference ranges for this test?
Normal reference ranges can vary by lab and may not be provided directly on your results. Your doctor will compare your levels to standards relevant to your age, gender, and overall health. Common ranges are often between 20–50 ng/mL (50–125 nmol/L), but these can differ by lab. Low levels may indicate deficiency, while very high levels could signal over-supplementation or other conditions.
How often should I get this test?
Your doctor may recommend this test if you have symptoms like fatigue, bone pain, or frequent infections, or if you live in a region with limited sunlight. Typically, adults may get tested every 1–2 years, but frequency depends on your risk factors (e.g., limited sun exposure, certain medical conditions).
Can vitamin D levels change quickly?
Yes, vitamin D levels can fluctuate due to changes in sun exposure, diet, or supplements. If you’ve recently changed your diet, started taking supplements, or moved to a different climate, let your doctor know—this may affect your test results.
  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 16, 2026. · Read our editorial policy