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Vitamin D, 25-Hydroxy [Mass concentration]

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

This blood test measures the amount of vitamin D in your body, specifically the form called 25-hydroxyvitamin D, which is the most reliable indicator of your overall vitamin D status.

Quick summary

["Vitamin D supports bone health, immune function, and muscle strength; low levels may indicate deficiency."]

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

Key facts at a glance

LOINC
14530-0
Short code
RUBV Ag Vag Ql IF
Synonyms
RUBV Ag Vag Ql IF
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
if
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 of vitamin D deficiency (like fatigue, bone pain, or frequent infections), a history of low vitamin D, limited sun exposure, or certain medical conditions (e.g., malabsorption). It’s also used to monitor vitamin D levels after treatment or supplementation.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the draw if your lab uses a fasting protocol. Wear a comfortable shirt for easy access to your arm.

What Happens During the Test?

A healthcare professional will insert a small needle into your arm to draw blood. The process takes about 5 minutes, and you may feel a brief pinch. The blood is sent to a lab for analysis.

What Are Possible Results?

Results are typically reported in nanograms per milliliter (ng/mL) or picomoles per liter (pmol/L). Your provider will interpret these numbers based on your health status and medical history.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Vitamin D Level

Frequently asked questions

What Does Low or High Vitamin D Mean?
Low levels may suggest deficiency, which can weaken bones, immune function, or increase risk of chronic diseases. High levels may indicate over-supplementation or certain conditions (e.g., kidney disease). Always discuss results with your provider.
How Often Should I Get This Test?
Your provider will recommend how often to retest based on your vitamin D status, lifestyle, and health goals. For example, adults with limited sun exposure may need testing every 6–12 months.
Can I Take Vitamin D Before the Test?
Yes, but avoid taking vitamin D supplements or consuming high-vitamin D foods (e.g., fatty fish) for 24 hours before the test to get an accurate measurement.
  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