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Serum Vitamin D (25-Hydroxyvitamin D) with Immunoassay Method

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

This test measures your levels of vitamin D in your blood, an important nutrient that helps your body absorb calcium and maintain strong bones.

Quick summary

["Vitamin D supports bone health and immune function; low levels may indicate deficiency or poor absorption."]

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

Key facts at a glance

LOINC
20458-6
Short code
RUBV IgG Ser-Imp
Synonyms
RUBV IgG Ser-Imp
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 healthcare provider may order this test to check if you have enough vitamin D, especially if you have symptoms like muscle weakness, bone pain, or a history of osteoporosis. It’s also used to monitor vitamin D levels in people who take supplements or have conditions that affect vitamin D absorption, such as certain digestive disorders.

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 part of a fasting panel. Bring any medications you’re taking, as some can affect vitamin D levels.

How the Test Works

A blood sample is taken from a vein in your arm. The lab uses an immunoassay method to detect and measure vitamin D in your serum.

What the Results Mean

Results help determine if your vitamin D levels are sufficient, insufficient, or deficient. Your provider will compare these results to your overall health and symptoms to guide treatment, such as supplements or lifestyle changes.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Vitamin D Level

Frequently asked questions

Your healthcare provider may ask about symptoms like fatigue, bone pain, or frequent infections, as well as any medications you take that could affect vitamin D levels.
Your test results will be reviewed in the context of your medical history, diet, and other health factors. Low vitamin D can increase the risk of bone-related conditions, while high levels may require monitoring to avoid toxicity.
How often will I need this test?
The frequency depends on your health status. If you have a known deficiency, your provider may recommend regular monitoring. Otherwise, it’s often done once or twice a year for adults at risk (e.g., limited sun exposure, older adults).
Can I eat or drink anything before the test?
If fasting is required, avoid food and liquids (except water) for 8–12 hours before the blood draw. If fasting isn’t needed, you can eat and drink normally, but avoid caffeine or alcohol before testing.
  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