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Vitamin B12 (Serum or Plasma Level)

Published: August 9, 2026Updated: August 16, 2026

This test measures your levels of vitamin B12, a crucial nutrient needed for nerve function and red blood cell production.

Quick summary

["Low levels may indicate deficiencies affecting your health."]

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

Key facts at a glance

LOINC
43852-3
Short code
FLUBV IgA Ser Ql
Synonyms
FLUBV IgA Ser Ql
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 to check for deficiencies, especially if you have symptoms like fatigue, numbness, or weakness. It can also help diagnose conditions like pernicious anemia or other vitamin deficiencies linked to poor absorption in the gut.

What to Expect Before the Test

No special preparation is needed. You may have blood drawn from a vein in your arm. If you’re taking certain medications (like certain antacids or proton pump inhibitors), your doctor may advise timing them around the test to avoid interference.

What the Results Mean

Results help determine if your vitamin B12 levels are within a healthy range. Very low levels may require further testing or treatment, such as vitamin B12 injections or dietary changes.

Common Causes of Low Levels

Vitamin B12 deficiency can result from poor diet (e.g., vegan/vegetarian diets), malabsorption issues (like pernicious anemia), or conditions affecting the stomach or intestines.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Vitamin B12 plays a vital role in maintaining nerve cells, DNA synthesis, and red blood cell production. Low levels can lead to neurological symptoms (e.g., tingling, memory issues) or anemia, while high levels are rarely a concern unless due to over-supplementation.

Short name

Vitamin B12

Frequently asked questions

Why might my vitamin B12 test be ordered even if I don’t have obvious symptoms?
Your doctor may recommend it as part of a routine checkup, especially if you have risk factors like a history of gastrointestinal diseases, strict dietary restrictions, or family history of deficiencies.
Can I take vitamin B12 supplements before the test?
Yes, but discuss it with your doctor first. Some supplements may affect test accuracy, so timing around the test is important.
What if my results are low?
If low, your doctor may suggest follow-up tests (like methylmalonic acid or homocysteine) or treatments like injections, dietary adjustments, or monitoring to prevent long-term effects.
  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