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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 (also called cobalamin) in your blood. Vitamin B12 is essential for nerve function, red blood cell production, and DNA synthesis.

Quick summary

["A low level may indicate a deficiency linked to poor absorption or dietary intake."]

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

Key facts at a glance

LOINC
42967-0
Short code
RUBV Ab Titr CSF
Synonyms
RUBV Ab Titr CSF
Category
chemistry
Sample
csf
Container
Sterile tube
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
1-2 mL
Stability
Immediate analysis required, Refrigerated: 1h
Hemolysis max
200
TAT
4–24 hours
Order
routine

Why Might You Need This Test?

Your doctor may order this test if you have symptoms like fatigue, weakness, numbness in hands/feet, or a smooth tongue. It’s also used to check for conditions like pernicious anemia, vitamin B12 deficiency anemia, or malabsorption disorders (e.g., celiac disease, atrophic gastritis).

How Is the Test Done?

A blood sample is taken from a vein in your arm. The blood is sent to a lab for analysis using an immunoassay method to detect vitamin B12 levels.

What to Expect Before the Test

No special preparation is needed, but avoid taking vitamin supplements (including multivitamins) 24 hours before testing to get an accurate result.

What Are Possible Results?

Results are compared to a reference range for healthy adults. Low levels may require further testing or treatment to address potential deficiencies.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin B12 Level

Frequently asked questions

What causes low vitamin B12 levels?
Low vitamin B12 levels can result from dietary deficiency (e.g., vegan diet without fortified foods), poor absorption due to conditions like pernicious anemia or gastric bypass surgery, or increased demand (e.g., pregnancy).
What symptoms might low vitamin B12 cause?
Symptoms may include fatigue, pale skin, weakness, numbness or tingling in hands/feet, balance problems, or memory issues. Deficiency can also lead to anemia and nerve damage over time.
How is vitamin B12 deficiency treated?
Treatment typically involves vitamin B12 injections or oral supplements. Lifestyle changes (e.g., fortified foods, B12-rich foods) may also be recommended, depending on the cause.
  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