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Serum Free Vitamin B12 (Serum Concentration)

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

This test measures the amount of vitamin B12 that is not bound to proteins in your blood, helping assess your overall B12 status.

Quick summary

["Free vitamin B12 helps ensure your body has enough of this essential nutrient for nerve and blood cell function."]

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

Key facts at a glance

LOINC
42955-5
Short code
SFV Ab Titr Ser
Synonyms
SFV Ab Titr Ser
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 Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms like fatigue, numbness, tingling in the hands or feet, or unexplained anemia. It may also be used to monitor vitamin B12 levels in people with certain medical conditions, such as pernicious anemia or malabsorption disorders.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into a vein in your arm to draw blood. This process usually takes a few minutes and may cause a slight pinch or discomfort.

What the Test Results Mean

Results help determine if your vitamin B12 levels are low, normal, or high. Low levels may indicate deficiencies or conditions affecting absorption, while high levels may require further investigation.

Common Conditions Monitored

This test is often used alongside total B12 levels to better understand vitamin B12 metabolism, especially in patients with suspected pernicious anemia, celiac disease, or other gastrointestinal disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Vitamin B12

Frequently asked questions

What causes low free vitamin B12 levels?
Low free vitamin B12 levels can result from conditions affecting vitamin absorption (e.g., atrophic gastritis, celiac disease), certain medications (e.g., proton pump inhibitors), or malabsorption syndromes. Lifestyle factors like poor diet may also contribute.
How is this test different from total B12?
Free vitamin B12 measures unbound B12, while total B12 includes both free and protein-bound forms. Free B12 testing can provide more nuanced insights into vitamin status, especially in patients with complex conditions.
Can diet affect free vitamin B12 results?
Yes, dietary intake of vitamin B12 (primarily from animal products) can influence both total and free B12 levels. However, free B12 testing is less affected by recent dietary changes compared to total B12.
  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