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Vitamin D, 25-Hydroxy [Serum]

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

This test measures the level of vitamin D in your blood, specifically the form called 25-hydroxyvitamin D, which is the active form your body uses to regulate calcium and bone health.

Quick summary

["Vitamin D levels help assess your risk for deficiencies that may affect bone health and other health conditions."]

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

Key facts at a glance

LOINC
14546-6
Short code
MuV Ag Throat Ql IF
Synonyms
MuV Ag Throat Ql IF
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
if
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 Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms of low vitamin D, such as muscle weakness, bone pain, or frequent infections. It may also be used to monitor vitamin D levels in people with conditions like osteoporosis, malabsorption disorders, or those taking certain medications that affect vitamin D metabolism.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if it involves a blood draw, but this is not always required for this specific test. Bring any medications you’re currently taking to your appointment.

How the Test Works

A small amount of blood is drawn from a vein in your arm. The blood sample is then sent to a lab where it is analyzed to measure the concentration of 25-hydroxyvitamin D using a sensitive immunoassay method.

What the Results Mean

Results are typically reported in nanograms per milliliter (ng/mL) or picomoles per liter (pmol/L). While reference ranges vary slightly by lab, low levels may indicate a deficiency, while higher levels may suggest over-supplementation or other conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

25-Hydroxy Vitamin D (Serum)

Frequently asked questions

How long does it take to get my results?
Results are usually available within 1–3 business days, depending on your lab’s processing time. Your healthcare provider will discuss the results with you during your follow-up visit.
Can I take vitamin D supplements before the test?
If your provider ordered this test specifically for vitamin D levels, it’s best to avoid taking supplements for at least 2–4 weeks before testing to get an accurate measurement. Always follow your provider’s instructions.
What if my results are outside the normal range?
If your levels are low, your provider may recommend dietary changes, increased sun exposure, or supplements to raise them. If levels are high, further evaluation may be needed to rule out conditions like vitamin D poisoning or over-supplementation. Your provider will guide you on next steps based on your specific situation.
  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