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Vitamin B12 (Serum or Plasma Concentration)

Published: August 9, 2026Updated: August 17, 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

["Vitamin B12 supports energy levels and nerve health—low levels may indicate deficiencies or underlying health issues."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
103016-2
Short code
Silver Birch (rBet v) 1 IgE RAST
Synonyms
Silver Birch (rBet v) 1 IgE RAST
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
rast
CPT
84484
SNOMED
302774002
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 doctor may recommend this test if you have symptoms like fatigue, weakness, numbness, or tingling in your hands and feet. It could also be part of a routine checkup for older adults, individuals with certain medical conditions (like pernicious anemia or celiac disease), or those on long-term vitamin B12 supplements.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before drawing blood. If you’re on vitamin B12 supplements, check with your doctor first to avoid interfering with results.

What the Test Involves

A healthcare provider will draw blood from a vein in your arm. The blood sample will be sent to a lab for analysis. The process takes a few minutes and is generally comfortable.

What the Results Mean

Results help determine if your vitamin B12 levels are within a healthy range. Low levels may suggest deficiencies, while high levels could indicate other conditions or medications. Your doctor will interpret the results in the context of your symptoms and medical history.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Vitamin B12 Level

Frequently asked questions

What are the normal reference ranges for this test?
Normal reference ranges can vary by lab and testing method. Your doctor will provide specific guidance based on your results. Low vitamin B12 levels can lead to anemia, nerve damage, or cognitive issues, while very high levels may require further investigation for causes like certain medications or liver disease.
Can vitamin B12 levels change with diet?
Yes, diet plays a role. Foods rich in vitamin B12 include animal products (meat, fish, eggs, dairy), fortified foods, and supplements. Certain medical conditions (like malabsorption disorders) or medications can also affect absorption.
How often should I get this test?
Your doctor will determine the frequency based on your health status. Typically, older adults or those with risk factors (like chronic illness or poor diet) may need monitoring every few years. If you’re on long-term treatment for low vitamin B12, your doctor may schedule follow-up tests.
  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 17, 2026. · Read our editorial policy