What Is Total Vitamin B12?
Total Vitamin B12 (cobalamin) measures all forms of vitamin B12 circulating in your blood. B12 is an essential water-soluble vitamin required for DNA synthesis, red blood cell formation, and the proper functioning of the nervous system. In the blood, approximately 80% of B12 is bound to haptocorrin (an inactive carrier) and only 20% is bound to transcobalamin II (the active, cell-deliverable form).
Total B12 remains the most commonly ordered B12 test in the UK, though it has limitations - particularly in the borderline range (150–300 ng/L) where it can miss early deficiency. For this reason, many clinicians now recommend active B12 (holotranscobalamin) as the first-line test when available.
Why Is Total B12 Tested?
- Screen for B12 deficiency in patients with anaemia, particularly macrocytic (large red cell) anaemia
- Investigate neurological symptoms: peripheral neuropathy, cognitive decline, depression, or balance problems
- Assess nutritional status in vegans, vegetarians, elderly patients, and those with malabsorption
- Monitor B12 replacement therapy (injections or supplements)
- Investigate unexplained fatigue, glossitis (sore tongue), or mouth ulcers
- Part of routine health screening in populations at risk of deficiency
Normal Ranges
| Category | Total B12 (ng/L or pg/mL) | Interpretation |
|---|---|---|
| Normal | 300 – 900 | Sufficient B12 stores |
| Borderline | 150 – 300 | Possible deficiency - active B12 or MMA testing recommended |
| Deficient | Below 150 | B12 deficiency likely - treatment recommended |
| Elevated | Above 900 | May indicate supplementation, liver disease, or myeloproliferative disorder |
Reference ranges may vary between laboratories. The borderline zone (150–300) is clinically challenging - up to 30% of patients in this range have functional deficiency.
Check Your Total Vitamin B12 Levels at Home
The Core Health 45 includes Total Vitamin B12 testing along with 44 other biomarkers. Results in 2 working days with a free at-home phlebotomist visit.
View Core Health 45 →Causes of Low Total B12
- Dietary deficiency: Vegan and strict vegetarian diets are the most common cause in younger adults
- Pernicious anaemia: Autoimmune destruction of gastric parietal cells and intrinsic factor - the most common cause in the elderly
- Malabsorption: Coeliac disease, Crohn's disease, small intestinal bacterial overgrowth (SIBO)
- Gastric conditions: Atrophic gastritis, H. pylori, partial gastrectomy, or bariatric surgery
- Medications: PPIs (omeprazole, lansoprazole), metformin, colchicine, and some anticonvulsants
- Age-related decline: Stomach acid production decreases with age, reducing B12 absorption
- Pregnancy and lactation: Increased demand can deplete maternal stores
Causes of High Total B12
- B12 supplementation or injections: The most common benign cause of elevated total B12
- Liver disease: Hepatocellular damage releases stored B12 into the bloodstream
- Myeloproliferative disorders: Polycythaemia vera, chronic myeloid leukaemia, and hypereosinophilic syndrome
- Kidney disease: Reduced renal clearance of B12 carrier proteins
- Autoimmune conditions: Some inflammatory states elevate haptocorrin-bound B12
Note: Unexplained high B12 without supplementation warrants investigation, as it can be a marker for underlying liver or haematological disease.
How to Maintain Healthy B12 Levels
- Eat B12-rich foods regularly: Liver, sardines, salmon, beef, eggs, milk, and cheese
- Supplement if vegan: Cyanocobalamin 10–25 µg daily or 1,000 µg twice weekly is the standard recommendation
- Use fortified foods: Fortified plant milks, nutritional yeast, and breakfast cereals
- Get injections if needed: Pernicious anaemia requires intramuscular hydroxocobalamin injections for life
- Review medications: Long-term PPI or metformin users should have B12 monitored annually
- Test folate too: B12 and folate deficiency can coexist and mask each other
When Should You Get Tested?
- You are vegan or vegetarian and not supplementing B12
- You have persistent tiredness, weakness, or breathlessness
- You experience neurological symptoms (tingling, numbness, poor balance, memory problems)
- Your blood count shows macrocytic anaemia (high MCV)
- You are over 65 and have not had recent B12 testing
- You take PPIs, metformin, or other medications affecting B12 absorption
Which Lola Health Tests Include Total B12?
- Peak Insights - includes both total and active B12 for the most complete assessment
- Vital Check — includes B12 as part of a comprehensive health screen
- Core Health — essential health screening with B12
Check Your Vitamin B12 Levels
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Test This Biomarker at Home
This biomarker is included in our Vitamin B12 (Active) Test and Core Health 45 — results in 2-3 working days with GP-reviewed insights.
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