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Serum or plasma concentration of **vitamin B12 (cobalamin)**

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

["Vitamin B12 helps prevent anemia and nerve damage; low levels may indicate deficiency or underlying health concerns."]

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

Key facts at a glance

LOINC
34250-1
Short code
Silver Birch (rBet v) 4 IgE Qn
Synonyms
Silver Birch (rBet v) 4 IgE Qn
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 this test if you have symptoms like fatigue, weakness, numbness, or tingling in your hands and feet. It can also be used to check for vitamin B12 deficiency, especially in people who follow strict vegetarian or vegan diets, have stomach or intestinal issues, or take certain medications that affect absorption.

What to Expect Before the Test

No special preparation is needed unless instructed by your doctor. You may have blood drawn from a vein in your arm. If you’re on a blood thinner, let your doctor know before the test.

What the Results Mean

Results can help determine if you have a vitamin B12 deficiency or other conditions affecting absorption. Your doctor will compare your results to standard ranges and discuss them with you.

Common Causes of Low or High Levels

Low vitamin B12 levels may be caused by poor diet, stomach disorders (like pernicious anemia), or conditions that affect absorption. High levels are less common but can occur with certain genetic disorders or long-term vitamin B12 supplements.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Vitamin B12 Level

Frequently asked questions

Is there anything I should do to prepare?
No special preparation is required unless your doctor advises otherwise. If you’re on blood-thinning medications, mention them to your healthcare provider before the test.
How long will it take to get my results?
Results are typically available within a few days to a week, depending on your lab’s processing time. Your doctor will explain what they mean in the context of your health.
Can I eat or drink before the blood draw?
You can eat and drink normally unless your doctor specifies otherwise. Avoid alcohol for 24 hours before the test if possible, as it may affect blood composition.
  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