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Vitamin B12 (Serum or Plasma Concentration)

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

This test measures the level of vitamin B12, an essential nutrient needed for healthy nerve function and red blood cell production.

Quick summary

["Low levels may indicate deficiencies or health conditions requiring medical attention."]

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

Key facts at a glance

LOINC
44577-5
Short code
FLUBV Ag Nose Ql
Synonyms
FLUBV Ag Nose Ql
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 doctor may order a vitamin B12 test to check for deficiencies, especially if you have symptoms like fatigue, numbness, or weakness. It can also help diagnose conditions like pernicious anemia or other gastrointestinal disorders that affect nutrient absorption.

What to Expect Before the Test

No special preparation is usually needed. You may have a blood sample drawn from a vein in your arm. If you’re taking certain medications (like certain antacids or proton pump inhibitors), your doctor may advise timing them around the test.

What the Results Mean

Results are compared to a general reference range for healthy adults. Very low levels may need further testing or evaluation of underlying causes, such as dietary issues, malabsorption problems, or certain medical conditions.

Common Causes of Low or High Levels

Low vitamin B12 levels can result from poor diet, conditions affecting stomach acid or intrinsic factor (like atrophic gastritis), or certain medications. High levels are less common but may occur with long-term vitamin B12 supplements or rare genetic disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Vitamin B12 deficiency can lead to neurological issues (e.g., tingling, balance problems) and anemia, which may cause fatigue or shortness of breath. Early detection and treatment (often with injections or supplements) can prevent long-term damage.

Short name

Vitamin B12

Frequently asked questions

Will I need to fast before this test?
No fasting is required for this blood test. However, if you’re on medications that affect vitamin levels (like certain antacids), your doctor may recommend timing them around the test.
How long will it take to get my 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 questions about your results.
Can I take vitamin supplements before the test?
If your doctor hasn’t instructed otherwise, avoid taking high-dose vitamin B12 supplements (especially oral or injectable forms) for 24 hours before the test, as they may affect results.
  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