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Vitamin B12 (Serum) – Mass Concentration

Published: August 9, 2026Updated: August 17, 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

["Low levels may indicate deficiencies linked to nerve damage or anemia."]

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

Key facts at a glance

LOINC
54377-7
Short code
Vit B12 Fld-mCnc
Synonyms
Vit B12 Fld-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 Matters

Vitamin B12 is a critical nutrient for maintaining healthy cells, especially in your nervous system and blood. Low levels can cause fatigue, weakness, or neurological issues. This test helps doctors check if you’re at risk for deficiency, which can develop from poor diet, certain medications, or conditions like pernicious anemia.

What to Expect Before the Test

No special preparation is needed, but you may fast for 8–12 hours before the draw if instructed by your provider. Bring your test results or a list of medications to your appointment.

How the Test Works

A blood sample is taken from a vein in your arm. The lab then uses a specialized method to measure the exact amount of vitamin B12 in your serum.

Possible Results and Next Steps

If your results are low, your doctor may recommend dietary changes, supplements, or further testing to identify the cause. High levels may require monitoring for conditions like vitamin B12 toxicity (rare).

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 Level

Frequently asked questions

Could low vitamin B12 levels affect my pregnancy?
Yes, vitamin B12 deficiency can harm fetal development if untreated. Women who are pregnant or planning pregnancy should discuss this test with their doctor, especially if they have risk factors like poor diet or certain medical conditions.
What if my test shows normal levels but I still feel tired?
Tiredness isn’t always linked to vitamin B12 alone. Other factors—like iron, folate, or thyroid issues—could be involved. Your doctor may order additional tests to explore other causes.
Do I need to avoid certain foods before the test?
No specific foods should be avoided, but you may need to fast for a set period if your lab instructions specify it. Always follow your healthcare provider’s 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 17, 2026. · Read our editorial policy