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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 nerve damage and anemia; low levels may indicate deficiencies or underlying health issues."]

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

Key facts at a glance

LOINC
44535-3
Short code
HTLV I Ab Ser Donr Ql
Synonyms
HTLV I Ab Ser Donr Ql
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 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 may also be used to diagnose or monitor conditions such as pernicious anemia, vitamin B12 deficiency, or malabsorption disorders like celiac disease or Crohn’s disease.

What to Expect Before the Test

No special preparation is needed for this blood test. You may have a small needle inserted into your arm to draw blood. If you’re on blood thinners, let your doctor know before the test.

What the Test Results Mean

Results can help determine if you have a vitamin B12 deficiency or other conditions affecting your blood or nerves. Your doctor will interpret the results in relation to your symptoms and overall health.

Common Conditions Linked to Low Vitamin B12

Low vitamin B12 levels can be linked to conditions like pernicious anemia (a type of autoimmune disorder), poor diet (especially in vegetarians/vegans), or digestive issues that reduce absorption.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin B12 Level

Frequently asked questions

What Are My Symptoms If My Vitamin B12 Level Is Low?
Symptoms of low vitamin B12 may include fatigue, weakness, numbness or tingling in the hands and feet, dizziness, memory problems, or mood changes. Some people may not notice symptoms until the deficiency is severe.
How Is Vitamin B12 Deficiency Treated?
Treatment typically involves vitamin B12 supplements (oral, injections, or nasal sprays) to restore levels. Lifestyle changes, such as a balanced diet (if diet-related), may also help. Follow-up tests are often needed to monitor progress.
Can Vitamin B12 Levels Be Too High?
Very high vitamin B12 levels are rare but can occur with certain medications, kidney disease, or rare genetic conditions. Your doctor will discuss results and any follow-up steps if needed.
  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