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Vitamin D (25-hydroxy) Serum Mass Concentration

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of vitamin D in your blood, specifically the form called 25-hydroxyvitamin D, which is the active form your body uses to maintain bone health and support overall wellness.

Quick summary

["Your blood vitamin D levels help assess whether you’re getting enough of this essential nutrient."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
87671-4
Short code
Vitamin D3 Spec-mCnt
Synonyms
Vitamin D3 Spec-mCnt
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
30
Ref high
100
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 This Test Matters

Vitamin D is crucial for bone health, immune function, and muscle strength. Low levels may indicate deficiencies that could lead to conditions like osteoporosis, muscle weakness, or increased infection risk. This test helps doctors determine if you need supplements or dietary adjustments.

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 protocol. Wear a comfortable shirt for easy access to your arm.

How the Test Works

A small blood sample is taken from your arm. The sample is then analyzed in a lab to measure the precise amount of 25-hydroxyvitamin D, which reflects your overall vitamin D status.

Possible Results and Next Steps

Results are typically reported in nanograms per milliliter (ng/mL). If your levels are low, your doctor may recommend increasing sun exposure, dietary changes (e.g., fatty fish, fortified foods), or supplements under medical guidance.

Reference range

NCBI: Vitamin D 30-100 ng/mL (sufficient)N/A

Specimen: serum

Fasting for 8-12 hours preferred for some tests. Inform about supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Vitamin D Blood Test

Frequently asked questions

What does my vitamin D level tell me about my health?
Low levels may signal vitamin D deficiency, which can affect bone health, immune function, and even mood. High levels may indicate over-supplementation or certain medical conditions. Your doctor will interpret results in the context of your overall health and symptoms.
How often should I get this test?
Vitamin D testing frequency depends on your risk factors (e.g., limited sun exposure, dark skin, or certain medical conditions). Typically, adults with no risk factors may get tested every 1–2 years, while others may need more frequent checks.
Can I take vitamin D supplements without testing?
It’s safer to consult your doctor first, especially if you’re taking supplements. High doses can cause toxicity, and testing ensures your levels are balanced for your needs.
  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 17, 2026. · Read our editorial policy