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Serum Vitamin D (25-hydroxyvitamin D) by Immunoassay

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

This test measures the amount of vitamin D in your blood, which is important for bone health and other bodily functions. Low levels may indicate deficiency, which can affect muscle strength, immunity, and bone density.

Quick summary

["Check your vitamin D levels to prevent deficiency and support overall health."]

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

Key facts at a glance

LOINC
13279-5
Short code
RUBV IgG sp1 Ser-aCnc
Synonyms
RUBV IgG sp1 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 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 obesity or liver disease.

Who Might Need This Test?

People who may need this test include those with suspected vitamin D deficiency, pregnant or breastfeeding individuals, older adults (since vitamin D absorption declines with age), or those with conditions that affect vitamin D metabolism.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it’s part of a larger blood draw. Wear comfortable clothing and bring any medications you’re currently taking.

What Happens During the Test?

A healthcare provider will draw blood from a vein in your arm. The process is quick and typically painless, though you may feel a slight pinch. The blood sample is then sent to a lab for analysis using an immunoassay method.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

This test helps diagnose or monitor vitamin D deficiency, which can lead to complications like osteoporosis, muscle weakness, or increased risk of infections. It also guides treatment decisions, such as vitamin D supplements or dietary adjustments.

Short name

Vitamin D Level

Frequently asked questions

What are the normal results?
There is no single 'normal' range for vitamin D levels because they can vary based on age, ethnicity, and other factors. Your results will be compared to your specific lab’s reference range, and your provider will interpret them in the context of your health.
How long does it take to get the results?
Results are usually available within 1–3 business days, depending on your lab and healthcare provider’s workflow. You’ll typically receive a call or letter with your results, or your provider will discuss them during a follow-up visit.
Can I eat or drink anything before the test?
If your test is part of a fasting blood draw, avoid food and liquids (except water) for 8–12 hours before the test. If it’s a non-fasting test, you can eat and drink normally, but check with your provider for specific instructions.
  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