Wellness . Symptoms guide
Vitamin B12 Deficiency: Symptoms and Testing
Quick answer
B12 deficiency can cause fatigue, hair shedding, brain fog, low mood, tingling or numbness, and in severe cases neurological damage. It is particularly common in vegans, vegetarians, older patients and after gastric surgery. Testing before supplementing matters because supplements can mask the deficiency in routine blood tests.
This patient information is being clinically reviewed by our team. The factual content draws on UK guidance (NHS, NICE, British Association of Dermatologists, and other specialist society guidance where cited).
What this might be
- Vegan or vegetarian diet. B12 is almost exclusively in animal products.
- Pernicious anaemia. Autoimmune loss of stomach factor needed for absorption.
- Metformin and PPI use. Both reduce B12 absorption over time.
- Coeliac disease and Crohn disease. Reduced absorption.
When to seek urgent advice
If any of the following apply, please contact your GP or NHS 111 rather than waiting for private bloodwork.
- Numbness or tingling in hands or feet
- Difficulty walking or unsteadiness
- Memory problems
Common features that suggest this
- Persistent fatigue
- Hair shedding
- Pale skin or yellow tinge
- Sore, red tongue
- Tingling in hands or feet
- Memory or concentration problems
Recommended tests
Same-day appointments at our Harley Street clinic, results clinician-reviewed.
Need a marker not in these panels? Build a custom panel and a GMC-registered clinician will design one for you.
Markers your clinician will commonly look at
These are the individual blood markers in the recommended panels above. Click any to read what it measures, its UK reference range, and what high or low values mean.
Testing advice
No fasting. If you have been taking B12 supplements, results will reflect supplemented status; some clinicians suggest pausing oral B12 for several weeks before testing if your prescriber agrees.
Common questions
What should B12 levels be?
UK laboratory ranges vary but typically sit around 200 to 900 ng/L (equivalent to roughly 148 to 665 pmol/L). NICE NG239 (March 2024) defines confirmed B12 deficiency as below 180 ng/L (133 pmol/L), with 180 to 350 ng/L treated as indeterminate. The local laboratory range should be used in interpretation, and borderline results may need repeat testing or further tests (active B12, MMA) if symptoms are present.
Do I need injections or are tablets enough?
Depends on cause. Dietary deficiency responds to high-dose oral B12. Pernicious anaemia and post-gastric-surgery deficiency may need injections. Bloodwork is the start of the decision.
Related symptoms
Sources and further reading
This page provides general information only and is not a substitute for medical advice. A GMC-registered clinician will review your results and tailor any recommendations to you personally.