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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

["Checks if you have enough vitamin B12 for your body’s needs."]

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

Key facts at a glance

LOINC
77384-6
Short code
FLUBV Ag BAL Ql IF
Synonyms
FLUBV Ag BAL Ql IF
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
if
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 This Test Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms like numbness or tingling in your hands and feet, weakness, memory problems, or an unusual appetite. It may also be done to diagnose or monitor conditions like pernicious anemia, vitamin B12 deficiency, or certain gastrointestinal 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 test if it involves drawing blood from a vein. If you’re taking vitamin B12 supplements, ask your provider how to proceed.

How the Test Is Performed

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

What the Results Mean

Low levels may indicate vitamin B12 deficiency, which can affect how your body uses energy and produces red blood cells. High levels are less common but could signal certain medical conditions or medications.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Vitamin B12 deficiency is often linked to poor absorption in the gut, chronic conditions like celiac disease or Crohn’s disease, or conditions that affect the stomach’s ability to release intrinsic factor (a protein needed for absorption). Early diagnosis and treatment can prevent serious complications like nerve damage or anemia.

Short name

Vitamin B12 Level

Frequently asked questions

What causes low vitamin B12 levels?
Low vitamin B12 levels can result from dietary deficiencies (rare in healthy diets), malabsorption (due to conditions like atrophic gastritis, celiac disease, or gastric bypass surgery), or certain medications that interfere with absorption.
How is vitamin B12 deficiency treated?
Treatment typically involves vitamin B12 supplements (injections, oral, or nasal forms) to restore levels. Lifestyle changes, such as a balanced diet rich in fortified foods or supplements, may also be recommended.
Can vitamin B12 levels be affected by medications?
Yes, some medications—like proton pump inhibitors, metformin, or certain antibiotics—may reduce vitamin B12 absorption. Always discuss potential interactions with your provider.
  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