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Serum or plasma concentration of vitamin D (25-hydroxyvitamin D)

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

This test measures your levels of vitamin D, a fat-soluble nutrient essential for bone health, immune function, and muscle strength. Low levels may indicate deficiency, which can affect overall health.

Quick summary

["Vitamin D levels help assess your risk for bone disorders, infections, and other health issues."]

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

Key facts at a glance

LOINC
110638-4
Short code
HCV RNA Msmt Tiss
Synonyms
HCV RNA Msmt Tiss
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
86803
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 is this test done?

Your healthcare provider may order this test if you have symptoms like fatigue, muscle weakness, bone pain, or if you’re at higher risk for deficiency—such as living far from the equator, having limited sun exposure, or having certain medical conditions like malabsorption disorders.

What does a low or high result mean?

Low levels may suggest vitamin D deficiency, which can lead to weakened bones, increased infection risk, or other health problems. High levels could indicate over-supplementation or certain medical conditions that need further evaluation.

How is the test performed?

A blood sample is taken from a vein in your arm. The sample is sent to a lab, where it’s analyzed to measure vitamin D levels using a sensitive immunoassay method.

What should I expect before the test?

No special preparation is needed, but inform your provider about any medications (including supplements) you’re taking, as some may affect results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin D blood test

Frequently asked questions

What are the normal reference ranges?
Reference ranges vary by lab, but typical ranges for serum 25-hydroxyvitamin D are between 20–50 ng/mL. Your provider will interpret results in the context of your health and symptoms.
How long does it take to get results?
Results are usually available within 1–3 business days, depending on your lab. Follow-up may be scheduled if further testing is needed.
Can I take vitamin D supplements before the test?
Yes, but avoid taking large doses (e.g., >4000 IU/day) for at least 2 weeks before testing to avoid skewing results. Always check with your provider first.
  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