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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, an essential nutrient needed for healthy nerve function and red blood cell production, in your blood.

Quick summary

["Vitamin B12 helps prevent nerve damage and anemia; 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
15052-4
Short code
Vit B12 USB SerPl-sCnc
Synonyms
Vit B12 USB SerPl-sCnc
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 Is This Test Done?

Your doctor may order this test if you have symptoms like fatigue, numbness, tingling in hands/feet, or unexplained anemia. It’s also used to screen for pernicious anemia, vitamin B12 deficiency due to poor diet, malabsorption issues (e.g., celiac disease), or certain medications interfering with absorption.

What to Expect Before the Test

No special preparation is needed. You’ll have a small needle inserted into your arm or vein for a blood draw. If you’re fasting, follow your doctor’s instructions, as diet can affect results.

What the Results Mean

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

Common Causes of Low Vitamin B12 Levels

Deficiencies often stem from poor diet (e.g., vegan/vegetarian diets lacking meat/fish), conditions like pernicious anemia (autoimmune), or digestive disorders (e.g., atrophic gastritis, Crohn’s disease). Medications like proton pump inhibitors may also reduce absorption.

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

What triggers a vitamin B12 test?
Symptoms like persistent fatigue, weakness, or unexplained numbness in hands/feet, or if your doctor suspects conditions like anemia, nerve disorders, or malabsorption issues.
How long does it take to get results?
Results are typically available within 1–3 business days, depending on your lab. Follow-up may be needed if results are outside the expected range.
Can diet affect vitamin B12 test results?
Yes; avoiding foods high in vitamin B12 (e.g., meat, eggs, dairy) for 2–3 days before testing may lower results. Your doctor may instruct fasting if needed.
  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