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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 in your blood. Vitamin B12 is essential for nerve function, red blood cell production, and DNA synthesis.

Quick summary

["Low levels may indicate deficiencies or underlying health concerns; high levels may need further evaluation."]

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

Key facts at a glance

LOINC
85801-9
Short code
FLUBV Yam Ag Titr Islt HAI
Synonyms
FLUBV Yam Ag Titr Islt HAI
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
hai
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 if you have symptoms like fatigue, numbness or tingling in your hands and feet, weakness, balance problems, or a history of poor nutrition, gastrointestinal issues, or certain medical conditions. It may also be part of routine blood work or screening for pernicious anemia or other deficiencies.

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 or medications, let your provider know.

What Happens During the Test?

A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a slight pinch, but the procedure is quick and usually painless. The blood sample is then sent to a lab for analysis.

What Are Possible Results?

Results are typically reported as a concentration value (e.g., in picograms per milliliter or picomoles per liter). Your provider will compare these results to standard ranges and discuss them with you.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Low vitamin B12 levels can cause anemia (reduced red blood cells), nerve damage, or cognitive issues. High levels may indicate overabsorption or certain genetic conditions. Your provider will interpret results in the context of your symptoms, medical history, and other tests.

Short name

Vitamin B12 Level

Frequently asked questions

What causes low vitamin B12 levels?
Low vitamin B12 levels can result from poor diet (e.g., vegan/vegetarian diets), conditions affecting absorption (e.g., pernicious anemia, celiac disease), or certain medications (e.g., proton pump inhibitors). Chronic kidney disease or malabsorption syndromes may also contribute.
How long does it take to get results?
Results are usually available within 1–3 business days, depending on your lab’s processing time. Your provider will contact you once they have the results and next steps.
Can I take vitamin B12 supplements if my levels are low?
If your provider confirms a deficiency, they may recommend oral supplements, injections, or dietary changes. Never self-treat without guidance, as excessive intake can sometimes cause other health issues.
  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