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Serum or plasma concentration of vitamin B12 (cobalamin)

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

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

Quick summary

["Vitamin B12 helps prevent nerve damage and supports blood health—low levels may signal deficiencies or underlying conditions."]

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

Key facts at a glance

LOINC
26642-9
Short code
JCV Ab Ser Ql
Synonyms
JCV Ab 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
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 essential for maintaining healthy nerve cells and preventing anemia. Low levels can cause fatigue, numbness, or balance issues. This test helps doctors diagnose deficiencies or related disorders early.

What to Expect Before the Test

No special preparation is needed unless instructed by your doctor. You may have a blood draw from a vein in your arm. If you’re on certain medications (like certain antacids or acid reducers), your doctor may advise timing around them.

Common Causes of Low or High Results

Low vitamin B12 levels often result from poor absorption (e.g., pernicious anemia, celiac disease), dietary lack, or conditions affecting the stomach or intestines. Rarely, high levels may indicate liver disease or certain genetic disorders.

What the Results Mean

Results below normal may prompt further testing (like a methylmalonic acid or homocysteine test) to check for absorption issues or other causes. High results alone usually don’t need follow-up unless symptoms like jaundice or liver issues are present.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Vitamin B12 Level

Frequently asked questions

What symptoms might this test help identify?
This test helps detect vitamin B12 deficiency, which can cause neurological symptoms (e.g., tingling, memory problems) or anemia (fatigue, weakness). Early diagnosis allows for treatment like B12 supplements or injections to prevent long-term nerve damage.
How often should I get this test?
Your doctor will determine frequency based on your symptoms, medical history, or risk factors (e.g., vegan diet, stomach surgery). Follow-up may include retesting if initial results are borderline or if symptoms persist.
Can diet affect this test?
Yes—high intake of vitamin B12 supplements or fortified foods (e.g., nutritional yeast) may temporarily raise results. Avoid overconsumption unless advised by your doctor, as excess isn’t harmful but may skew interpretation.
  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