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Serum or plasma concentration of vitamin D (25-hydroxyvitamin D)

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

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

Quick summary

["Vitamin D levels help prevent deficiencies that can weaken bones and raise disease risk."]

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

Key facts at a glance

LOINC
17520-8
Short code
RSV Spec Cult
Synonyms
RSV Spec Cult
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
organism-specific-culture
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 doctor may order this test to check if you have enough vitamin D, especially if you have symptoms like muscle pain, fatigue, or a history of bone problems. It’s also used in people with conditions like osteoporosis, kidney disease, or those who don’t get enough sunlight.

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 blood draw. Wear comfortable clothing and plan for the test to take about 15 minutes.

What Happens During the Test?

A healthcare provider will insert a small needle into a vein in your arm to draw blood. You may feel a slight pinch, but it’s over quickly. The blood is sent to a lab for testing.

What Are Possible Results?

Results are compared to a standard range, but exact numbers vary by lab. Low levels may need supplements or lifestyle changes, while very high levels could require medical review.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin D level

Frequently asked questions

Why might my vitamin D test be abnormal?
Low levels may suggest poor sun exposure, limited diet, or malabsorption issues (like celiac disease). High levels could result from over-supplementation or rare genetic conditions. Always discuss results with your doctor.
How long will it take to get my results?
Results are typically available within 1–3 business days, depending on your lab. Follow-up may be scheduled if further testing is needed.
Can I eat or drink before the test?
Yes, you can eat normally, but avoid caffeine or alcohol before the blood draw. Fasting is only required if instructed by your doctor.
  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