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Vitamin D (25-hydroxy) - Serum or Plasma

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

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

Quick summary

["Check your vitamin D levels to prevent deficiency-related issues like bone pain or fatigue."]

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

Key facts at a glance

LOINC
81292-5
Short code
Simple var type
Synonyms
Simple var type
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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?

Doctors may order this test if you have symptoms like muscle weakness, frequent fractures, or unexplained fatigue. It’s also common for people with limited sun exposure, certain medical conditions (e.g., celiac disease, kidney disease), or those taking medications that affect vitamin D absorption.

Who Might Need This Test?

Adults and children with suspected vitamin D deficiency, pregnant or breastfeeding women, older adults (who may have lower vitamin D levels naturally), or those with conditions that reduce vitamin D production (like dark skin or limited sun exposure).

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the blood draw if your test involves a different vitamin D marker (e.g., 25-hydroxy). Bring any medications you’re taking to your appointment.

What Happens During the Test?

A healthcare provider will draw blood from a vein in your arm. The process takes a few minutes, and you may feel a slight pinch. The blood is then sent to a lab for analysis.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin D Level

Frequently asked questions

What are the normal ranges for this test?
Reference ranges vary by lab and may include different forms of vitamin D (e.g., 25-hydroxy vs. 1,25-dihydroxy). Your doctor will provide your specific results and explain what they mean for you.
Can I take vitamin D supplements before the test?
If your doctor has instructed you to fast before the test, avoid vitamin D supplements or foods high in vitamin D (e.g., fatty fish) for 24 hours before drawing blood. If no fasting is required, ask your provider for guidance.
How long will it take to get my results?
Results are typically available within 1–3 business days, depending on your lab. Your doctor will discuss the findings with you during a follow-up visit.
  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