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Serum or plasma concentration of vitamin B12 (substance concentration)

Published: August 9, 2026Updated: August 16, 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

["Vitamin B12 helps prevent serious health issues like anemia or nerve damage."]

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

Key facts at a glance

LOINC
21592-1
Short code
VZV Ab Titr CSF
Synonyms
VZV Ab Titr CSF
Category
chemistry
Sample
csf
Container
Sterile tube
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
1-2 mL
Stability
Immediate analysis required, Refrigerated: 1h
Hemolysis max
200
TAT
4–24 hours
Order
routine

Why This Test Might Be Ordered

Your doctor may recommend this test if you have symptoms like fatigue, weakness, numbness, or tingling in your hands and feet. It could also be part of a routine checkup for people at higher risk of deficiency, such as those with certain dietary restrictions, gastrointestinal conditions, or those who have had stomach surgery.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it involves drawing blood from a vein. If you’re taking vitamin B12 supplements, check with your doctor first to avoid interfering with the results.

What Happens During the Test

A healthcare professional will draw blood from a vein in your arm using a small needle. The process is quick and typically painless. You may feel a brief pinch, but most people tolerate it well.

What the Results Mean

Results help determine if your vitamin B12 levels are too low, normal, or too high. Low levels may indicate a deficiency, which can be caused by poor absorption, certain medical conditions, or diet. High levels might suggest overconsumption or certain genetic conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin B12 Level

Frequently asked questions

How long does it take to get my results?
Results are usually available within 1–3 business days, depending on your lab and insurance. Your doctor will contact you once they’re ready to discuss your results.
Can I eat or drink anything before this test?
Most tests don’t require fasting, but if instructed by your doctor (especially for blood tests), avoid food and liquids for 8–12 hours before drawing blood. Always follow your healthcare provider’s specific instructions.
What are the most common causes of low vitamin B12 levels?
Common causes include poor diet (especially in vegetarians/vegans), conditions like pernicious anemia (autoimmune disorder affecting stomach function), gastric bypass surgery, or certain medications that interfere with absorption. If you suspect a deficiency, discuss your diet, medications, and symptoms with your doctor.
  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