Vitamin B12 Blood Test

What Is Vitamin B12?

A Vital Nutrient

Vitamin B12 (cobalamin) is a water-soluble vitamin essential for multiple systems in the body:

• It supports the production of healthy red blood cells
• Maintains neurological function and brain health by supporting healthy nerve cells
• Helps form and repair DNA
• Supports methylation and detoxification pathways

Your body can’t make B12 on its own, so you must get it from your diet (animal-based foods) or supplements. Absorption also depends on stomach acid and intrinsic factor, a protein secreted in your stomach. Only certain forms of B12 are biologically active and directly support these functions.

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How a Vitamin B12 Blood Test Works

A vitamin B12 blood test measures your vitamin B12 level in the bloodstream. It’s usually included as part of a broader blood work vitamin B12 panel alongside markers like:

• Methylmalonic acid (MMA): elevated levels suggest deficiency
• Homocysteine: high levels may also indicate poor B12 function
• Folate: checked alongside B12 as they work together; B12 and folate are often tested together because of their interrelated roles in cell health and metabolism

These supporting markers give a clearer picture when total B12 levels fall in the “borderline” range. Other blood tests may also be ordered alongside B12 testing for a comprehensive assessment, depending on your symptoms and medical history.

Why Get a Vitamin B12 Test?

1. Deficiency Is More Common Than You Think

Up to 15% of adults may be low in B12, especially:

• Adults over 50 (due to reduced stomach acid)
• Vegetarians or vegans
• People on long-term acid-blocking medications
• Those with gut conditions (e.g. coeliac or Crohn’s disease)

2. Symptoms Are Often Subtle or Overlooked

B12 deficiency can look like everyday stress or ageing:

• Fatigue, weakness, or brain fog
• Poor memory or concentration
• Numbness or tingling in hands/feet
• Pale skin, dizziness, or shortness of breath
• Mood issues (depression or irritability)

If left untreated, deficiency can cause irreversible nerve damage and serious cognitive decline.

3. It Impacts Multiple Systems

Low B12 is linked to:

• Anaemia: B12 is required for red blood cell formation
• Neurological disorders: including dementia and neuropathy; B12 is essential for the proper function of the nervous system
• Cardiovascular risk: elevated homocysteine raises heart disease risk; folic acid, along with B12, is sometimes considered for lowering homocysteine, though evidence for benefit is limited
• Infertility and birth defects: B12 is essential for DNA development

What Affects Your B12 Levels?

Diet

B12 is naturally found in animal products like:

• Red meat
• Eggs
• Fish and shellfish
• Dairy

Those avoiding animal products are at high risk for deficiency unless supplementing.

Gut Health

The digestive system plays a crucial role in B12 absorption, which relies on intrinsic factor and stomach acid. Parietal cells in the stomach lining secrete intrinsic factor, while hydrochloric acid helps release B12 from food proteins, allowing it to bind with intrinsic factor for absorption in the intestine. Conditions that impair this process include:

• Gastritis
• Pernicious anaemia, an autoimmune condition called pernicious anaemia that damages parietal cells in the stomach lining, reducing intrinsic factor production and leading to B12 deficiency
• Coeliac or Crohn’s disease
• Past gastric surgery

Medications

Certain drugs can deplete or interfere with B12 absorption:

• Metformin
• Proton pump inhibitors (PPIs)
• H2 receptor antagonists

Age

As you get older, your ability to absorb B12 from food declines. B12 deficiency in seniors is often underdiagnosed.

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Risk Factors and Prevention

Understanding the risk factors for vitamin B12 deficiency is the first step towards prevention. Certain groups are at increased risk, including those following a strict vegetarian diet, individuals who have undergone gastrointestinal surgery or gastric bypass, and people taking certain medications such as proton pump inhibitors. Conditions like celiac disease and Crohn’s disease can also interfere with the absorption of vitamin B12, raising the likelihood of deficiency. Additionally, a family history of pernicious anemia or previous issues with the stomach lining can further increase risk.

To help prevent vitamin B12 deficiency, it’s important to include animal products such as meat, fish, and dairy products in your diet, or to choose fortified foods like breakfast cereals and nutritional yeast if you follow a plant-based diet. Dietary supplements can be a practical solution for those unable to meet their needs through food alone. Staying alert to symptoms such as fatigue, neurological symptoms, or signs of megaloblastic anemia can prompt early testing and intervention. Maintaining normal vitamin B12 levels through a balanced diet and regular monitoring is key to supporting healthy red blood cells, nerve function, and overall well-being.

Preparing for Your B12 Test

• No fasting is usually required
• Avoid taking B12 supplements 24 hours before the test
• Inform your clinician of any medications
• It may be tested alongside folate, MMA, and homocysteine for a full picture

Understanding Your Vitamin B12 Test Results

B12 Levels Normal Range

• 148 - 590 pmol/L is the general lab range
• Below 110 pmol/L is considered deficient
• Above 590 pmol/L is considered elevated

Low B12 (Deficiency)

May cause:

• Anaemia
• Neuropathy (nerve pain or tingling)
• Fatigue, poor mood, and memory issues
• Increased homocysteine (cardiovascular risk)

Folate deficiency can also occur alongside B12 deficiency, compounding the risk of anemia and neurological symptoms.

High B12 Levels in Blood

Can be due to:

• Supplement use
• Liver dysfunction
• Liver disease
• Kidney disease
• Myeloproliferative disorders (rare)

Isolated elevated levels of vitamin B12 without symptoms or cause should be discussed with your doctor.

How to Improve Vitamin B12 Levels

1. Food Sources

• Liver and kidney
• Beef, chicken, and fish (especially salmon, sardines)
• Eggs and dairy (milk, cheese, yoghurt)

2. Supplements

• Cyanocobalamin: stable, common, cost-effective
• Methylcobalamin: active form, better absorbed in people with methylation issues
• Hydroxocobalamin: longer-acting form used in injections

Supplements are available orally, sublingually, or by injection (when absorption is impaired).

3. Address Underlying Issues

• Treat gut conditions
• Adjust medications where possible
• Monitor regularly if at risk

The Role of Healthcare Providers

Healthcare providers are essential partners in maintaining healthy vitamin B12 levels. If you experience symptoms of vitamin B12 deficiency or have risk factors such as a family history of pernicious anemia, your healthcare provider can order a blood test to check your vitamin B12 levels. If results are abnormal, further tests may be recommended to determine the underlying cause, such as issues with absorption or other medical conditions.

Beyond diagnosis, healthcare providers offer expert guidance on treatment options, which may include dietary supplements, vitamin B12 injections, or adjustments to your diet. They can help interpret your blood test results, explain what your levels mean, and develop a personalised treatment plan to address any deficiency. Regular check-ups and open communication with your healthcare provider ensure that any changes in your health are detected early, allowing for prompt treatment and prevention of complications like nerve damage or anemia. By working closely with your healthcare provider, you can take proactive steps to protect your health and maintain optimal vitamin B12 levels.

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Sources

1. National Institutes of Health (NIH) – Vitamin B12 Fact Sheet for Health Professionals‍

https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/

2. Harvard T.H. Chan School of Public Health – Vitamin B12

https://www.hsph.harvard.edu/nutritionsource/vitamin-b12/

3. British Medical Journal (BMJ) – Diagnosis of Vitamin B12 Deficiency: An Update

https://www.bmj.com/content/349/bmj.g5226

4. UpToDate – Clinical Manifestations and Diagnosis of Vitamin B12 and Folate Deficiency

https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-vitamin-b12-and-folate-deficiency