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Vitamin B12 (Serum or Plasma Mass Concentration)

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

This test measures the amount of vitamin B12, an essential nutrient needed for healthy red blood cells, nerve function, and DNA synthesis.

Quick summary

["Low levels may indicate deficiencies linked to fatigue, numbness, or digestive issues; high levels may require further evaluation."]

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

Key facts at a glance

LOINC
2922-3
Short code
Vit A Bld-mCnc
Synonyms
Vit A Bld-mCnc
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your doctor may order this test if you have symptoms like weakness, tingling in hands/feet, memory problems, or unexplained anemia. It’s also used to monitor vitamin B12 status in people with conditions like pernicious anemia, celiac disease, or those on certain medications.

What to Expect During the Test

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 a few days.

Common Causes of Low or High Levels

Low levels can result from poor diet, malabsorption issues (e.g., stomach or intestinal disorders), or certain medications. High levels may occur with long-term vitamin B12 supplements or genetic conditions.

Who Might Need This Test?

People at higher risk include those over 50, vegetarians/vegans, individuals with autoimmune diseases, or those with a history of stomach surgery.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin B12 Level

Frequently asked questions

How long does it take to get results?
Results are usually ready within 2–5 business days, depending on lab processing times. Your doctor will discuss them with you during your follow-up.
What does a low vitamin B12 level mean?
A low result suggests you may have a deficiency. Your doctor will assess symptoms and possibly order additional tests (e.g., methylmalonic acid or homocysteine) to pinpoint the cause.
Can I take supplements before the test?
Yes, but avoid high-dose supplements (e.g., >1000 mcg/day) for 2–4 weeks before testing to get an accurate measurement. Follow your doctor’s instructions.
  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