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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, which is important for nerve function and red blood cell production.

Quick summary

["Vitamin B12 helps prevent anemia and supports brain health; low levels may indicate deficiencies or underlying health concerns."]

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

Key facts at a glance

LOINC
8014-3
Short code
RUBV IgG Ser-aCnc
Synonyms
RUBV IgG Ser-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82784
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 a vitamin B12 test if you have symptoms like fatigue, weakness, numbness, or balance issues. It can also be part of screening for pernicious anemia, certain gastrointestinal conditions, or malabsorption disorders.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for a few hours before the blood draw if your test involves a specific timing (e.g., 24-hour urine). Bring any medications you’re taking to your appointment.

During the Test

A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch, but it only takes a few minutes. The blood sample is sent to a lab for analysis.

What the Results Mean

Results are compared to standard reference ranges for your age and sex. Low levels may signal vitamin B12 deficiency, while very high levels are rare but could indicate certain medical conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin B12 level

Frequently asked questions

What could cause abnormal results?
Low vitamin B12 levels can result from dietary deficiencies (e.g., vegan diets), malabsorption issues (e.g., celiac disease or atrophic gastritis), or conditions like pernicious anemia. High levels may indicate liver disease, certain cancers, or overconsumption of supplements.
How long will it take to get results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Your doctor will discuss them with you during your follow-up visit.
Can I take vitamin B12 supplements before testing?
Yes, but avoid taking high-dose supplements or oral vitamin B12 supplements 24–48 hours before testing, as this may affect accuracy. If you’re unsure, ask your doctor for guidance.
  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