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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, red blood cell production, and DNA synthesis.

Quick summary

["Low levels may indicate deficiencies or underlying health concerns needing attention."]

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

Key facts at a glance

LOINC
85690-6
Short code
RUBV Gentyp Spec
Synonyms
RUBV Gentyp Spec
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 if you have symptoms like fatigue, numbness, tingling in hands/feet, memory problems, or unexplained anemia. It’s also used to screen for pernicious anemia, certain gastrointestinal conditions, or malabsorption disorders.

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 draw if your lab uses a fasting protocol. Wear a loose shirt for easy access to your arm.

How the Test Works

A healthcare professional will draw blood from a vein in your arm. The sample is sent to a lab where it’s analyzed using an immunoassay method to detect vitamin B12 levels.

What the Results Mean

Results help determine if your vitamin B12 levels are within the normal range. Low levels may prompt further testing or treatment, such as vitamin B12 supplements or injections.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin B12 Level

Frequently asked questions

What Are Common Symptoms of Low Vitamin B12?
Common symptoms include fatigue, weakness, pale or yellowish skin, shortness of breath, dizziness, vision changes, and neurological issues like numbness or balance problems. Early diagnosis is key to preventing long-term nerve damage.
Can Diet Alone Fix a Vitamin B12 Deficiency?
Dietary sources like meat, fish, eggs, and dairy can help, but some people (e.g., vegetarians/vegans) may need supplements or fortified foods. Absorption issues, such as those in stomach disorders, often require medical intervention.
How Often Should I Get This Test?
Your provider will decide based on your symptoms, medical history, or risk factors (e.g., chronic gastritis, celiac disease). Typically, follow-up tests are scheduled if initial results are low or abnormal.
  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