Vitamin B12 supports normal blood and nervous-system function. NICE advises that symptoms and signs vary and often have causes other than B12 deficiency. A clinician considers your symptoms, medical history, medicines, diet and risk factors before interpreting a test.[1]
This page provides evidence-only information. It does not diagnose B12 deficiency, decide your treatment route or replace an urgent medical assessment.
When to seek urgent assessment
Do not wait for a routine test if symptoms are severe or worsening
Call 999 for a life-threatening emergency, severe breathing difficulty, collapse or severe chest pain. Seek urgent NHS advice for new or worsening confusion, marked weakness, problems with walking or balance, or other acute neurological symptoms.
Possible symptoms and risk factors
Possible symptoms include unexplained fatigue, a sore or red tongue, vision changes, problems with memory or concentration, pins and needles, numbness, weakness, balance problems and changes found on a blood count. These features do not point to one diagnosis by themselves.[1] [2]
Diet and nutrition
A diet low in B12-containing or fortified foods can contribute, but diet may not be the only cause.
Absorption and health conditions
Autoimmune gastritis, coeliac disease and some gastrointestinal operations can affect B12 absorption.
Medicines and substances
Some medicines and recreational nitrous oxide are listed by NICE as risk factors requiring a careful assessment.
Medical and family history
An autoimmune condition, family history, prior radiotherapy or surgery can shape the clinical question.
Testing and interpreting results
NICE advises using total B12 or active B12 as an initial test for most people with suspected deficiency. The suitable first test can differ in pregnancy and where nitrous oxide use is the suspected cause. Samples should be taken before replacement starts where possible.[1]
Supplements, injections or patches can affect a result. A combined oral contraceptive pill can also lower total B12 without necessarily indicating deficiency. A clinician may use laboratory information and additional tests in selected circumstances. A number on a report is not a diagnosis on its own.[1]
Why the cause affects treatment
NICE describes treatment plans that vary with the cause of the deficiency. Dietary deficiency, suspected or confirmed malabsorption, medicine-related deficiency and nitrous oxide use require different clinical decisions. Some people with an irreversible cause need lifelong replacement.[1]
The NHS also explains that injections or tablets may be used, depending on the cause and whether neurological symptoms are present. A prescribing clinician should agree the route, dose, review schedule and safety advice with you. This page does not provide a self-treatment regimen.[3]
Frequently asked questions
Can tiredness mean I have vitamin B12 deficiency?
Tiredness has many possible causes. NICE lists unexplained fatigue as one possible symptom or sign, but a clinician considers symptoms with risk factors and other information before selecting tests.
Can B12 deficiency happen without anaemia?
Yes. NICE advises clinicians not to rule out B12 deficiency solely because anaemia or macrocytosis is absent.
Does a low B12 result identify the cause?
No. A result may prompt further work to identify the cause, such as a dietary issue, absorption problem, medicine effect or another condition. The appropriate tests depend on the clinical picture.
Will I need tablets or injections?
Treatment depends on the cause, symptoms and circumstances. NICE describes both oral and intramuscular replacement pathways in selected situations. A prescribing clinician must decide the route and plan.
Related routes and information
References
- [1]NICE NG239: Vitamin B12 deficiency in over 16s: diagnosis and management
- [2]NHS: Vitamin B12 or folate deficiency anaemia symptoms
- [3]NHS: Vitamin B12 or folate deficiency anaemia treatment
Sources checked 30 August 2026. This evidence-only page does not replace individual assessment, diagnosis or urgent medical care.