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

Quick summary

["Vitamin B12 helps prevent nerve damage and supports blood cell health—low levels may indicate deficiencies or other health concerns."]

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

Key facts at a glance

LOINC
55881-7
Short code
Vit B12b SerPl-sCnc
Synonyms
Vit B12b 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 This Test Matters

Your doctor may order this test if you have symptoms like fatigue, numbness, tingling in the hands/feet, or unexplained anemia. It can also help diagnose conditions like pernicious anemia, vitamin B12 malabsorption, or certain gastrointestinal disorders.

What to Expect Before the Test

No special preparation is needed, but inform your provider about any medications (especially those affecting blood or vitamin absorption) or recent dietary changes. Blood is drawn from a vein, usually in your arm.

What the Results Mean

Results help determine if your vitamin B12 levels are within the normal range. Low levels may prompt further testing or treatment (e.g., vitamin B12 supplements or injections). High levels may require investigation for underlying causes.

Common Causes of Low Vitamin B12

Deficiencies can arise from poor diet (e.g., vegan/vegetarian diets), malabsorption issues (e.g., atrophic gastritis, celiac disease), or conditions like pernicious anemia. Rarely, medications or certain medical treatments can contribute.

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.

Vitamin B12 deficiency can lead to neurological symptoms (e.g., memory loss, balance problems) or anemia, impairing energy and cognitive function. Early detection allows for timely intervention to prevent long-term damage.

Short name

Vitamin B12 Level

Frequently asked questions

What if my vitamin B12 level is low?
If your test result is low, your doctor may recommend follow-up tests (e.g., methylmalonic acid or homocysteine) to identify the cause. Treatment often starts with vitamin B12 supplements (oral, injections, or nasal sprays) under medical supervision.
Does diet affect vitamin B12 test results?
Yes, dietary intake can influence results. Avoid extreme dietary changes (e.g., sudden veganism) before testing, as it may affect your baseline level. Your doctor may advise timing around meals if dietary history is relevant.
How often should I get this test?
Frequency depends on your health status. People with known deficiencies, certain medical conditions, or those on long-term supplements may need monitoring every few months. Regular check-ups with your provider will guide timing.
  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