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Fluorometric Immunoassay for Vitamin B12 (Serum)

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

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

Quick summary

["Vitamin B12 helps prevent nerve damage and anemia; low levels may indicate deficiency."]

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

Key facts at a glance

LOINC
5866-9
Short code
FLUBV Ag Spec Ql IA
Synonyms
FLUBV Ag Spec Ql IA
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ia
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 healthcare provider may order this test if you have symptoms like fatigue, numbness, tingling, or weakness, or if you have conditions like pernicious anemia, poor diet, or certain medications that affect vitamin B12 absorption. It may also be part of routine blood work or screening for deficiencies.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into your arm to draw blood. If you’re on certain medications (like proton pump inhibitors), your provider may advise adjusting timing or discussing alternatives.

What the Results Mean

Results help determine if your vitamin B12 levels are within a healthy range. Low levels may prompt further testing or treatment, while normal levels suggest no immediate concern. Your provider will discuss results in the context of your overall health.

Common Causes of Low Vitamin B12

Vitamin B12 deficiency can arise from poor diet (e.g., vegan/vegetarian diets), conditions affecting absorption (like atrophic gastritis), or certain medications. Chronic conditions like Crohn’s disease or kidney disorders may also contribute.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

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

Short name

Vitamin B12 Level (Serum)

Frequently asked questions

What if my vitamin B12 test is low?
If your results are low, your doctor may recommend follow-up tests (like methylmalonic acid or homocysteine) to assess nerve damage. Treatment often starts with B12 supplements (oral or injections) to restore levels and improve symptoms.
How long does it take to get results?
Results are typically available within 1–3 business days, depending on your lab. Your doctor will contact you once they’re ready for review.
Can I eat or drink before the blood draw?
You can eat and drink normally before the test, but avoid caffeine or heavy meals right before drawing blood to minimize discomfort.
  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