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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 absorb calcium and maintain bone health. Low levels may indicate deficiency, which can affect muscle function, bone strength, and overall health.

Quick summary

["Vitamin D levels help assess bone health and prevent deficiencies that may cause fatigue or muscle weakness."]

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

Key facts at a glance

LOINC
10129-5
Short code
ST wave MD L-V6
Synonyms
ST wave MD L-V6
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ekg
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 like muscle pain, frequent infections, or if you’re at higher risk for vitamin D deficiency, such as living far from the equator, having limited sun exposure, or having certain medical conditions like kidney disease or obesity.

Who Might Need This Test?

Common reasons include routine check-ups for older adults, pregnant women, people with dark skin (who need more sun exposure to produce vitamin D), or those with conditions that affect vitamin D metabolism.

What to Expect Before the Test

No special preparation is needed. You may have blood drawn from a vein in your arm. If you’re taking vitamin D supplements, check with your provider first to avoid interfering with test results.

What the Results Mean

Results are compared to standard ranges for your age and health status. Very low levels may require supplements or dietary changes, while very high levels could indicate overuse of supplements or certain medical conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin D level (25-OH vitamin D)

Frequently asked questions

How often should I get this test?
Typically, vitamin D levels are checked every 1–2 years if you’re at risk for deficiency, or as recommended by your provider. If you’re pregnant, have chronic conditions, or take supplements, follow your healthcare team’s advice.
What are the normal ranges for this test?
There isn’t a single universal range—it varies by lab and individual factors like age, ethnicity, and health status. Your provider will interpret results based on your specific needs.
Can diet or supplements affect this test?
Yes, foods rich in vitamin D (like fatty fish, fortified dairy, or egg yolks) and supplements can influence results. If you’re taking supplements, discuss timing with your provider to avoid false readings.
  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