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Serum Vitamin D (25-Hydroxyvitamin D) Concentration

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

This test measures the amount of vitamin D in your blood, which helps your body use calcium and maintain strong bones. Low levels may increase your risk of bone-related health issues.

Quick summary

["Vitamin D helps your body absorb calcium and maintain strong bones; low levels may raise risks for bone disorders."]

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

Key facts at a glance

LOINC
13281-1
Short code
RUBV IgG CSF-aCnc
Synonyms
RUBV IgG CSF-aCnc
Category
chemistry
Sample
csf
Container
Sterile tube
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82784
Specimen volume
1-2 mL
Stability
Immediate analysis required, Refrigerated: 1h
Hemolysis max
200
TAT
4–24 hours
Order
routine

Why This Test Matters

Vitamin D is essential for bone health and immune function. Your doctor may order this test if you have symptoms like muscle weakness, bone pain, or if you’re at higher risk for vitamin D deficiency (e.g., limited sun exposure, certain medical conditions, or dietary habits).

What to Expect During Testing

A small blood sample is drawn from a vein in your arm. The sample is sent to a lab for analysis. Results are typically available within 1–3 business days.

What the Results Mean

Results are compared to standard reference ranges for vitamin D levels. While exact ranges can vary by lab, low levels may indicate deficiency, which could affect bone health or immune function. Your doctor will discuss results in the context of your overall health.

Common Causes of Low or High Levels

Low vitamin D levels can result from insufficient sun exposure, poor diet, certain medications, or medical conditions like kidney disease. High levels may be due to over-supplementation or rare genetic disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Vitamin D Level

Frequently asked questions

How long does it take to see changes in vitamin D levels after treatment?
Changes in vitamin D levels may take weeks to months to normalize after starting treatment, depending on the severity of deficiency and the type of intervention (e.g., supplements, sunlight exposure). Your doctor may recommend follow-up tests to monitor progress.
Can vitamin D levels be affected by medications?
Yes, certain medications—such as anticonvulsants, some steroids, or medications for HIV—can interfere with vitamin D metabolism, potentially lowering blood levels. Always discuss medications with your doctor.
What symptoms might indicate vitamin D deficiency?
Symptoms of deficiency may include fatigue, muscle weakness, bone pain, or frequent infections. However, many people have no symptoms until deficiency is severe. If you suspect deficiency, talk to your doctor about 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