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

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

This test measures your body’s level of vitamin D, an important nutrient that helps your bones stay strong and supports overall health.

Quick summary

["Vitamin D levels help assess your risk for deficiencies and related health issues."]

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

Key facts at a glance

LOINC
104457-7
Short code
VZV IgA CSF Ql IA
Synonyms
VZV IgA CSF Ql IA
Category
chemistry
Sample
csf
Container
Sterile tube
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ia
CPT
82784
Specimen volume
1-2 mL
Stability
Immediate analysis required, Refrigerated: 1h
Hemolysis max
200
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your doctor may order this test if you have symptoms like fatigue, muscle weakness, or bone pain, or if you’re at higher risk for deficiency (e.g., limited sun exposure, certain medical conditions, or dietary habits). It’s also used to monitor vitamin D levels in people taking supplements or those with 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 test if it’s done on an empty stomach. Bring any medications you’re currently taking, as some may affect results.

How the Test Is Performed

A blood sample is drawn from a vein in your arm by a healthcare professional. The blood is then sent to a lab where it’s analyzed to measure vitamin D levels.

What the Results Mean

Results are typically reported as a numerical value representing the concentration of vitamin D in your blood. Lower levels may indicate deficiency, while higher levels may suggest excess intake or metabolic issues. Your doctor will interpret results in the context of your overall health.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin D level

Frequently asked questions

What Are Common Causes of Abnormal Results?
Low vitamin D levels can be caused by limited sun exposure, poor diet, certain medical conditions (like kidney or liver disease), or medications that interfere with absorption. High levels may result from overuse of supplements or certain genetic conditions.
How Often Should I Get This Test?
Your doctor will determine how often you need testing based on your health status, risk factors, and symptoms. For example, adults with osteoporosis or those with limited sun exposure may need more frequent checks.
Can I Take Vitamin D Supplements Without Checking My Levels First?
It’s best to discuss supplement use with your doctor before taking vitamin D, especially if you have kidney disease or take certain medications. High doses can be harmful, and testing helps ensure you’re getting the right amount.
  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