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Vitamin B12 (Serum or Plasma) Concentration

Published: August 9, 2026Updated: August 17, 2026

This test measures the level of vitamin B12 (also called cobalamin) 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 and nerve damage."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
61535-1
Short code
Years vit B12 PhenX
Synonyms
Years vit B12 PhenX
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
200
Ref high
900
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
phenx
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 doctor may order 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, especially if you have conditions like pernicious anemia, celiac disease, or a strict vegetarian/vegan diet that may affect vitamin B12 absorption.

Who Might Need This Test?

People at higher risk for vitamin B12 deficiency include those with conditions that interfere with absorption (like atrophic gastritis), those who follow plant-based diets, or those taking certain medications that reduce stomach acid.

What to Expect During the Test

A blood sample is taken from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause discomfort. The test is quick and doesn’t require special preparation.

What the Results Mean

Low levels of vitamin B12 may indicate deficiency, which can lead to health problems over time. High levels might suggest other conditions or medications. Your doctor will interpret the results in the context of your symptoms and medical history.

Reference range

NCBI: Vitamin B12 200-900 pg/mLN/A

Specimen: serum

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin B12

Frequently asked questions

What Are Common Symptoms of Low Vitamin B12?
Symptoms of vitamin B12 deficiency can develop slowly and may include fatigue, weakness, pale skin, shortness of breath, numbness or tingling in hands and feet, balance problems, memory loss, or mood changes. Early detection is important to prevent long-term nerve damage or anemia.
How Long Does It Take to Get Results?
Results are typically available within 1 to 3 business days, depending on your lab’s processing time. Your doctor will discuss the results with you during your follow-up visit.
Can I Take Vitamin B12 Supplements Before the Test?
It’s best to avoid taking vitamin B12 supplements or high-dose multivitamins before the test unless instructed by your doctor. This ensures the test reflects your current vitamin B12 levels accurately.
  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 17, 2026. · Read our editorial policy