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Serum or plasma concentration of free vitamin B12 (cobalamin)

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

This test measures the amount of vitamin B12 (a crucial nutrient for nerve and blood cell function) that is not bound to proteins in your blood. Low levels may indicate deficiencies or conditions affecting absorption.

Quick summary

["Vitamin B12 helps prevent nerve damage and supports red blood cell production—low levels can cause fatigue or neurological issues."]

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

Key facts at a glance

LOINC
43839-0
Short code
FLUBV IgG Ser Ql
Synonyms
FLUBV IgG 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 This Test Might Be Ordered

Your doctor may recommend this test if you have symptoms like weakness, numbness, memory problems, or unusual fatigue. It’s also checked in people with conditions like pernicious anemia, celiac disease, or those on certain medications that interfere with vitamin B12 absorption.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the draw if your lab uses a specific method. Bring any medications or supplements you take regularly to your appointment.

How the Test Works

A small blood sample is taken from your arm. The lab measures the free (unbound) form of vitamin B12 using an immunoassay or similar method to detect its presence in your serum or plasma.

What the Results Mean

Results are compared to a reference range for your age and health status. Low levels may signal vitamin B12 deficiency, while high levels could indicate liver disease or certain medications. Your doctor will discuss these findings with you.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Vitamin B12 Level

Frequently asked questions

What could cause low vitamin B12 levels?
Low vitamin B12 levels can result from dietary deficiency (e.g., vegan diets), impaired absorption (e.g., atrophic gastritis, pernicious anemia), or conditions like kidney disease. Chronic alcohol use or certain medications (e.g., metformin) may also contribute.
What could cause high vitamin B12 levels?
Elevated free vitamin B12 is less common but may occur in liver disease, certain cancers, or with long-term use of some medications. Your doctor will investigate further if results are unusually high.
How often should I get this test?
Vitamin B12 levels are typically checked if symptoms or risk factors (like chronic illness) suggest a deficiency. Follow your doctor’s advice—some people need regular monitoring if they have conditions affecting absorption.
  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