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

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

This test measures the amount of vitamin D in your blood, which helps your body use calcium and maintain strong bones. Low levels may indicate deficiency, which can affect bone health and other body functions.

Quick summary

["Vitamin D levels help prevent deficiencies that could lead to health risks like bone disorders or weakened immunity."]

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

Key facts at a glance

LOINC
29536-0
Short code
WNV IgM Ser-aCnc
Synonyms
WNV IgM Ser-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82784
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 doctor may order this test if you have symptoms like bone pain, muscle weakness, or if you’re at higher risk for vitamin D deficiency—such as not getting enough sunlight, having limited sun exposure, or having certain medical conditions.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if it involves a blood draw. Wear comfortable clothing and plan for a short visit to a lab or clinic.

What Happens During the Test?

A healthcare provider will draw blood from a vein in your arm. The sample is sent to a lab for analysis, where it’s measured for vitamin D levels using an immunoassay method.

What Are the Results Mean?

Results are typically reported as a concentration of vitamin D in the blood. Your doctor will compare these results to standard ranges and discuss them with you based on your health history and symptoms.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin D level

Frequently asked questions

How long does it take to get my vitamin D test results?
Results are usually available within 1–3 business days, depending on your lab’s processing time. Your doctor will contact you once they’re ready for review.
Can I take vitamin D supplements before my test?
If your doctor prescribed supplements, follow their instructions. If you’re unsure, avoid taking them 2–3 weeks before testing to get an accurate measurement.
What if my vitamin D level is low?
If your results show low levels, your doctor may recommend lifestyle changes (like more sun exposure or dietary adjustments) or supplements to help restore balance. They’ll work with you to create a plan tailored to your needs.
  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