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Vitamin B12 (Serum or Plasma Level)

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of vitamin B12 in your blood, an essential nutrient for nerve function and red blood cell production.

Quick summary

["Vitamin B12 helps prevent serious health issues like anemia or nerve damage."]

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

Key facts at a glance

LOINC
2171-7
Short code
Vit B12 USB SerPl-mCnc
Synonyms
Vit B12 USB SerPl-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
200
Ref high
900
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 This Test Might Be Ordered

Your doctor may recommend a vitamin B12 test if you have symptoms like fatigue, weakness, numbness, tingling, or trouble with balance and coordination. It may also be checked during routine blood work, if you have conditions like pernicious anemia, or if you’re at higher risk due to diet (e.g., vegan/vegetarian), certain medications, or long-term stomach issues.

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 fasting protocol. Bring any medications or supplements you’re taking, as some (like vitamin B12 supplements) could affect results.

What the Test Involves

A healthcare provider will draw blood from a vein in your arm. It usually takes a few minutes, and you may feel a slight pinch. The blood sample is sent to a lab for analysis.

What the Results Mean

Low results may indicate vitamin B12 deficiency, which can cause health problems over time. High results are less common but may signal other conditions like certain cancers or liver disease. Your doctor will discuss results in the context of your symptoms and medical history.

Reference range

NCBI: Vitamin B12 200-900 pg/mLN/A

Specimen: serum

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin B12 (B12)

Frequently asked questions

How long does it take to get results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Follow-up with your doctor is needed to interpret results and plan next steps.
What causes vitamin B12 deficiency?
Deficiency can result from poor diet (e.g., not eating enough animal products), conditions affecting absorption (like pernicious anemia or stomach surgery), or certain medications. Lifestyle factors like smoking or alcohol use may also play a role.
Can I take vitamin B12 supplements to fix low levels?
Yes, oral supplements or injections can raise vitamin B12 levels. However, your doctor may recommend monitoring or other treatments (like dietary changes or medications) to address the root cause of your deficiency.
  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