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Vitamin D (25-hydroxy) with Immunoassay (Serum/Plasma)

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

This test measures the level of vitamin D in your blood, specifically the form that your body converts from sunlight exposure or diet into its active form.

Quick summary

["Vitamin D helps maintain strong bones and supports overall health, including immune function."]

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

Key facts at a glance

LOINC
103049-3
Short code
Mugwort (nArt v) 3 IgE RAST
Synonyms
Mugwort (nArt v) 3 IgE RAST
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
rast
CPT
84484
SNOMED
302774002
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, which is important for preventing conditions like osteoporosis, rickets, or muscle weakness. It’s also used to diagnose or monitor vitamin D deficiency, especially in people with limited sun exposure, certain medical conditions, or those taking medications that affect vitamin D levels.

What to Expect Before the Test

No special preparation is needed for this blood test. You may be asked to fast for 8–12 hours before the draw if your lab requires it, but always follow your provider’s instructions. Wear a comfortable shirt with sleeves rolled up for easy access.

What Happens During the Test?

A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause significant discomfort. The blood sample is then sent to a lab for analysis using an immunoassay method to detect vitamin D levels.

What the Results Mean

Results are typically reported as a concentration of vitamin D in the blood. Low levels may indicate deficiency, while higher levels could suggest overabsorption or certain conditions. Your provider will interpret the results in relation to your health and symptoms.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

25-Hydroxy Vitamin D (25(OH)D)

Frequently asked questions

How does vitamin D deficiency affect health?
Vitamin D deficiency can lead to weakened bones (osteoporosis or rickets in children), muscle pain or weakness, fatigue, and an increased risk of certain infections. It may also be linked to other conditions like autoimmune diseases or certain cancers, though research is ongoing. Your provider will assess results alongside your overall health to guide treatment if needed.
What causes vitamin D levels to be low?
Low vitamin D levels can result from limited sun exposure, poor diet (low in fatty fish, fortified foods), certain medical conditions (like Crohn’s disease or celiac disease), obesity, or medications that interfere with vitamin D metabolism. Age, skin tone, and living in regions with limited sunlight can also play a role.
Can vitamin D levels be too high?
Yes, very high vitamin D levels may cause symptoms like nausea, vomiting, or excessive thirst. Chronic high levels can lead to calcium buildup in organs or kidney problems. Your provider will monitor results closely and adjust recommendations if necessary, such as limiting supplements or dietary sources.
  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