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Vitamins

Active Vitamin B12

Active Vitamin B12 measures the bioavailable B12 your cells can utilise. For active individuals, B12 may support oxygen transport, energy metabolism, and recovery. This test could help optimise your performance-related nutritional status.

Doctor's Assessment Included

Reference Ranges

See the value that applies to you:

Choose male or female — this range differs by sex.

Enter your age — this range changes with age.

This range also depends on context such as cycle phase or sample material; the highlighted rows apply to your group.

Male Your group
pmol/l
Low 35 Normal 108 High
Female Your group
pmol/l
Low 35 Normal 108 High

Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.

Check your own value

What It Measures

This test measures holotranscobalamin, the active fraction of vitamin B12 bound to transcobalamin II. This is the only form of B12 that can be taken up by all cells in your body for essential metabolic processes.

Why It Matters

Active individuals may have higher B12 demands due to increased metabolic activity. Low active B12 could be associated with reduced endurance, slower recovery, and impaired red blood cell production. Consider discussing your levels with a sports medicine provider.

When to Test

Testing may be recommended if you follow a vegetarian or vegan diet, experience unexplained fatigue or tingling in your extremities, are over 50, or have digestive conditions that could affect nutrient absorption. Consult your healthcare provider for guidance.

Symptoms

Low Levels

Some people with low active B12 levels may experience fatigue, weakness, tingling or numbness in hands and feet, difficulty concentrating, mood changes, and pale skin. A healthcare provider should evaluate persistent symptoms.

High Levels

Elevated active B12 levels are less commonly associated with symptoms but may sometimes indicate underlying conditions such as liver disease or certain blood disorders. Your healthcare provider can help interpret high results in context.

Lifestyle Tips

Including B12-rich foods such as meat, fish, eggs, and dairy in your diet may help support healthy levels. Those on plant-based diets might consider discussing supplementation with their healthcare provider. Regular monitoring can help track your status over time.

Frequently Asked Questions

What is the difference between active B12 and total B12?
Active B12 measures only the form your cells can use, while total B12 includes both active and inactive forms. Active B12 is generally considered a more reliable early indicator of deficiency by many healthcare professionals.
Who may be at risk for low active B12?
People following vegan or vegetarian diets, older adults, those with digestive conditions like Crohn's disease or celiac disease, and individuals taking certain medications such as metformin or proton pump inhibitors may have an increased risk.
How often should I test my active B12 levels?
Testing frequency depends on your individual circumstances. Your healthcare provider can recommend an appropriate schedule based on your diet, medical history, and any symptoms you may be experiencing.

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