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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, which can affect bone health and other body functions.

Quick summary

["Vitamin D levels help prevent deficiencies that can lead to bone problems or other health risks."]

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

Key facts at a glance

LOINC
25479-7
Short code
S rectivirgula IgG Qn
Synonyms
S rectivirgula IgG Qn
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82784
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 if you have symptoms like muscle weakness, bone pain, or if you’re at higher risk for vitamin D deficiency (e.g., limited sun exposure, certain medical conditions, or dietary habits). It’s also used to monitor treatment for conditions like osteoporosis or rickets.

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 specific method. Wear a loose shirt for easy access to your arm.

What Happens During the Test?

A healthcare provider will insert a small needle into your vein (usually in your arm) to draw blood. You may feel a slight pinch, but it usually takes only a few minutes. The blood is then sent to a lab for testing.

What Are Possible Results?

Results are typically reported as a numerical value (e.g., ng/mL or nmol/L) representing your vitamin D level. Your doctor will interpret these results in relation to your health and symptoms.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin D level

Frequently asked questions

What Does a Low or High Level Mean?
Low levels of vitamin D may signal deficiency, which can weaken bones, increase infection risk, or contribute to chronic conditions like heart disease. High levels can sometimes indicate over-supplementation or liver/kidney issues, though this is rare. Your doctor will discuss results with you based on your medical history.
How Often Should I Get This Test?
Your doctor will determine how often you need testing based on your health status, age, and risk factors. Some people (e.g., those with kidney/liver disease or limited sun exposure) may need more frequent checks.
Can I Take Vitamin D Supplements Without Checking First?
It’s best to check with your doctor before taking supplements. High doses can be harmful, and your doctor can guide you on safe levels based on your test results.
  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