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Serum or plasma concentration of vitamin B12 (cobalamin)

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

This test measures the amount of vitamin B12, an essential nutrient important for nerve function and red blood cell production, in your blood.

Quick summary

["Vitamin B12 helps prevent nerve damage and supports healthy blood cells."]

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

Key facts at a glance

LOINC
5330-6
Short code
RUBV Ab Ser HAI-aCnc
Synonyms
RUBV Ab Ser HAI-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
hai
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 doctor may order this test to check for vitamin B12 deficiency, which can cause symptoms like fatigue, numbness, or weakness. It may also be used to diagnose conditions like pernicious anemia, certain gastrointestinal disorders, or malabsorption issues.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it involves drawing blood from a vein. If you’re taking vitamin B12 supplements, your doctor may advise stopping them temporarily.

How the Test Is Performed

A healthcare provider will draw blood from a vein in your arm using a small needle. You may feel a brief pinch, but the procedure is quick and typically painless. The blood sample is then sent to a lab for analysis.

What the Results Mean

Results help determine if your vitamin B12 levels are low, normal, or high. Low levels may indicate deficiency, while high levels could suggest certain medical conditions or lab artifacts. Your doctor will interpret the results in the context of your symptoms and overall health.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Vitamin B12 Level

Frequently asked questions

What Are Common Causes of Low Vitamin B12 Levels?
Low vitamin B12 levels can result from dietary deficiencies (e.g., vegan diets), conditions affecting absorption (like atrophic gastritis or celiac disease), or certain medications. Symptoms may include fatigue, tingling in hands/feet, or balance issues.
What If My Results Are Abnormal?
If your results show low vitamin B12, your doctor may recommend dietary changes, supplements, or further testing (like a Schilling test) to identify the cause. High levels may require follow-up to rule out errors or unrelated conditions.
How Often Should I Get This Test?
Your doctor will decide based on your health status. Typically, repeat testing is done if symptoms persist or if you have known risk factors (e.g., chronic illnesses, certain medications).
  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