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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, an essential nutrient important for nerve function and red blood cell production, in your blood.

Quick summary

["Vitamin B12 helps prevent nerve damage and supports healthy blood cells."]

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

Key facts at a glance

LOINC
44574-2
Short code
FLUBV Ag Trachea Ql IF
Synonyms
FLUBV Ag Trachea 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 Is This Test Done?

Your healthcare provider may order a vitamin B12 test to check for deficiencies, which can cause fatigue, numbness, weakness, or other symptoms. It may also be used to diagnose conditions like pernicious anemia, nerve disorders, or malabsorption issues.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if your blood is drawn from a vein, but this depends on your lab instructions. If you’re taking vitamin B12 supplements, check with your provider first.

How the Test Is Performed

A small needle is inserted into a vein in your arm, and blood is collected into a tube. The sample is then sent to a lab for analysis.

What the Results Mean

Low levels may indicate a deficiency, while very high levels (rare) could suggest certain medical conditions or supplements. Your provider will interpret results in the context of your symptoms and other tests.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin B12 Level

Frequently asked questions

A vitamin B12 deficiency can lead to serious health issues, including anemia, nerve damage, and cognitive problems. Early detection and treatment (such as supplements or injections) can prevent long-term complications.
What happens if my vitamin B12 level is low?
If your results are low, your doctor may recommend dietary changes, supplements, or further testing to identify the cause (e.g., poor absorption, dietary restrictions). Follow-up tests might include checking folate levels or stomach function.
Can I take vitamin B12 supplements without checking my levels first?
It’s best to avoid high-dose supplements without medical advice, as excessive intake can be harmful. Your provider will guide you on safe levels based on your test results and health needs.
Some labs may require fasting for 8–12 hours before drawing blood, but always confirm with your lab or provider before the test.
  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