Skip to content

Vitamin B12 (Serum or Plasma Concentration)

Published: August 9, 2026Updated: August 16, 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

["Low B12 can cause fatigue, numbness, or anemia; high levels may indicate certain medical conditions."]

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

Key facts at a glance

LOINC
50694-9
Short code
RUBV Ab Titr Ser HAI
Synonyms
RUBV Ab Titr Ser 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 This Test Might Be Ordered

Your doctor may recommend this test if you have symptoms like weakness, tingling in hands/feet, memory issues, or if you have conditions like pernicious anemia, celiac disease, or long-term vegan diet. It’s also checked during routine blood work or if you’re at higher risk for deficiencies.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the draw if your lab uses a specific protocol. Bring your medical history and any medications to your appointment.

What the Results Mean

Results are compared to a reference range for healthy adults. Very low levels may indicate deficiency, while very high levels could signal conditions like liver disease or certain cancers.

Common Causes of Abnormal Results

Deficiencies often stem from poor diet, malabsorption (e.g., from stomach issues or surgery), or certain medications. Overproduction may result from liver problems or excessive intake.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

B12 Level

Frequently asked questions

What symptoms might indicate a B12 deficiency?
Symptoms can include fatigue, pale skin, shortness of breath, numbness/tingling in extremities, memory loss, or balance problems. If you experience these, discuss them with your doctor.
How is B12 deficiency treated?
Treatment often involves B12 supplements (oral, injections, or nasal sprays) or dietary changes. Your doctor may monitor levels and adjust treatment based on your response.
Can high B12 levels be dangerous?
Extremely high levels are rare but may signal underlying conditions like liver disease or tumors. Your doctor will interpret results in context with your health history.
  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