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Vitamin B12 (Serum or Plasma Concentration)

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

This test measures the amount of vitamin B12 in your blood. Vitamin B12 is essential for nerve function and red blood cell production.

Quick summary

["Your B12 levels help identify deficiencies that may affect your energy, nerve health, or blood health."]

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

Key facts at a glance

LOINC
50709-5
Short code
FLUBV Ab Titr Ser HAI
Synonyms
FLUBV Ab Titr Ser HAI
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?

Doctors may order a B12 test if you have symptoms like fatigue, numbness or tingling in your hands and feet, weakness, memory problems, or unusual food cravings. It’s also used to check for pernicious anemia, certain digestive disorders, or malabsorption issues.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the draw if your blood is collected early in the morning. Wear a loose shirt for easy access.

What Happens During the Test?

A healthcare provider will insert a small needle into your arm to draw blood. You may feel a brief pinch, but it usually doesn’t cause significant discomfort. The blood is then sent to a lab for analysis.

What Are the Possible Results?

Results are compared to standard reference ranges, but exact values can vary by lab. Low levels may indicate a deficiency, while higher levels may require further investigation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Low vitamin B12 levels can lead to anemia, nerve damage, or cognitive issues. High levels may suggest liver disease, certain medications, or other conditions. Early detection helps prevent long-term health problems.

Short name

B12 Level

Frequently asked questions

What causes low vitamin B12 levels?
Low B12 levels can result from poor diet (e.g., vegan/vegetarian diets), conditions like pernicious anemia, digestive disorders (e.g., celiac disease), or medications that interfere with absorption.
How long does it take to get results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Follow-up with your doctor if you have concerns.
Can I take supplements before the test?
Avoid high-dose vitamin B12 supplements or fortified foods for at least 2 weeks before testing, as they may affect results. Always check with your doctor first.
  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