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25-Hydroxyvitamin D (25(OH)D) Serum

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

This test measures the amount of vitamin D in your blood, specifically the form that your body converts from sunlight or diet into an active form for bone and immune health.

Quick summary

["Vitamin D helps maintain bone health and supports immune function."]

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

Key facts at a glance

LOINC
49543-2
Short code
Deprecated Calcidiol+Calciferol SerPl-mC
Synonyms
Deprecated Calcidiol+Calciferol SerPl-mC
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?

Your healthcare provider may order this test to check if you have enough vitamin D, which can be important for preventing conditions like osteoporosis, rickets, or muscle weakness. It’s also used to monitor vitamin D levels in people with conditions like malabsorption or those taking supplements.

What Does a Low or High Level Mean?

Low levels may indicate vitamin D deficiency, which can affect bone health and immune function. High levels can sometimes signal over-supplementation or other underlying health concerns, though this is less common.

How Is the Sample Collected?

A small amount of blood is drawn from a vein in your arm by a healthcare professional. The blood is sent to a lab for testing.

What Are Common Causes of Low Vitamin D?

Factors like limited sun exposure, certain medical conditions (such as celiac disease or Crohn’s disease), obesity, or taking medications that interfere with vitamin D absorption can lead to lower levels.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Vitamin D deficiency is linked to weakened bones, fatigue, and increased infection risk. Proper levels are crucial for overall health, especially in older adults or those with limited sun exposure.

Short name

Vitamin D Level

Frequently asked questions

How long does it take to get results?
Results are typically available within 1 to 3 business days, depending on your lab’s processing time.
Is there anything I should do before the test?
No special preparation is needed, but you may be asked to fast for 8–12 hours before the blood draw if instructed by your provider.
Can I take vitamin D supplements before the test?
If your provider prescribed supplements, check with them first to avoid interfering with test accuracy. If you’re unsure, ask your provider whether to stop taking them temporarily.
  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