Skip to content

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 is important for bone health and overall well-being.

Quick summary

["Vitamin D helps maintain strong bones and supports immune function."]

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

Key facts at a glance

LOINC
31964-0
Short code
RUBV Ag UrnS Ql
Synonyms
RUBV Ag UrnS Ql
Category
chemistry
Sample
urine
Container
Sterile urine container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
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 low due to limited sun exposure, certain medical conditions, or poor diet. It’s also used to monitor vitamin D levels in people taking supplements or those with conditions like osteoporosis or rickets.

What Does a Low or High Level Mean?

Low levels of vitamin D may indicate a risk for bone-related problems, weakened immunity, or muscle weakness. High levels can sometimes cause calcium buildup in the blood or kidneys and may require medical attention.

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 is analyzed to measure vitamin D levels using a specialized immunoassay method.

What Are Common Causes of Vitamin D Deficiency?

Vitamin D deficiency is often caused by limited sun exposure, certain skin conditions (like melanoma), obesity, or conditions that affect the ability to absorb nutrients (like celiac disease). Dietary sources like fatty fish, fortified dairy, and supplements can also influence levels.

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 Results?
There is no single reference range for all labs, as it can vary by lab and individual factors. Your healthcare provider will interpret the results in relation to your health status and symptoms.
How Often Should I Get This Test?
Your healthcare provider will determine how often you need this test based on your health needs, risk factors, and medical history. Some people may need it annually, while others may need it more or less frequently.
What Can I Do to Maintain Healthy Vitamin D Levels?
To support healthy vitamin D levels, get regular sunlight exposure (short periods), eat foods rich in vitamin D, and consider supplements if advised by your doctor. Avoid excessive sun exposure to prevent skin damage.
  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