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Vitamin D, 25-Hydroxy [Serum]

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

This test measures the level of vitamin D in your blood, specifically the form that your body converts from sunlight exposure or diet to use for bone health and other functions.

Quick summary

["Vitamin D levels help ensure your bones stay strong and support overall health."]

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

Key facts at a glance

LOINC
14531-8
Short code
RUBV Ag UrnS Ql IF
Synonyms
RUBV Ag UrnS Ql IF
Category
chemistry
Sample
urine
Container
Sterile urine container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
if
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms like bone pain, muscle weakness, or if you’re at risk for vitamin D deficiency—such as not getting enough sunlight, having limited sun exposure, or having certain medical conditions that affect vitamin D absorption.

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 provider’s instructions. Bring any medications you’re taking to your appointment.

What the Test Measures

The test detects 25-hydroxy vitamin D, the form of vitamin D that circulates in your blood and reflects your overall vitamin D status. Lower levels may indicate deficiency, while higher levels may suggest over-supplementation or other conditions.

How the Results Are Used

Your results help determine if you need to adjust your diet, sunlight exposure, or vitamin D supplements to maintain healthy levels. Your provider will interpret the results in relation to your symptoms and medical history.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Vitamin D deficiency is linked to weakened bones, increased risk of fractures, and potential immune system issues. Proper levels support muscle function, immune health, and may reduce inflammation. Results guide treatment plans for deficiency or excess.

Short name

25-Hydroxy Vitamin D

Frequently asked questions

What causes vitamin D levels to be low?
Low vitamin D levels can result from limited sun exposure, poor diet, certain medical conditions (like malabsorption disorders), or medications that interfere with vitamin D metabolism.
How long does it take to get results?
Results are typically available within 1–3 business days after your blood sample is processed. Your healthcare provider will discuss them with you during your follow-up visit.
Can I take vitamin D supplements before the test?
It’s best to avoid taking vitamin D supplements 2–3 days before the test unless instructed otherwise by your provider, as this may affect the accuracy of your 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