Blood test
Vitamin B12 Test
A vitamin B12 test is a blood test that checks your B12 level, which is needed for healthy nerves and blood cells. It helps diagnose deficiency, a common and treatable cause of tiredness.
Quick answer
Vitamin B12 Test: what it is and what the results mean
This blood test measures the level of vitamin B12, a nutrient essential for making red blood cells and keeping the nervous system healthy. It is often checked alongside folate.
- Why it is done: It is used to investigate tiredness, anaemia, nerve symptoms such as tingling, and memory problems, and to diagnose and monitor B12 deficiency, which can result from diet or from problems absorbing the vitamin.
- Understanding results: A low B12 can cause a particular type of anaemia and nerve problems and needs treatment, either by injections or tablets depending on the cause.
What it is
This blood test measures the level of vitamin B12, a nutrient essential for making red blood cells and keeping the nervous system healthy. It is often checked alongside folate.
Why it is done
It is used to investigate tiredness, anaemia, nerve symptoms such as tingling, and memory problems, and to diagnose and monitor B12 deficiency, which can result from diet or from problems absorbing the vitamin.
What to expect
A standard blood sample is taken from the arm; fasting is not usually required.
Understanding the results
A low B12 can cause a particular type of anaemia and nerve problems and needs treatment, either by injections or tablets depending on the cause. Borderline results are sometimes rechecked or investigated further, and B12 is read alongside folate and a full blood count.
Good to know
Risks and limitations
The test carries the minor risks of any blood test. B12 levels do not always reflect the amount active in the body, so occasionally further tests are used when the picture is unclear.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
Vitamin B12 Test: frequently asked questions
What are the symptoms of low vitamin B12?
Low B12 can cause tiredness, breathlessness, a sore tongue, pins and needles, and sometimes memory or balance problems. It is diagnosed with a blood test and is treatable.
How is vitamin B12 deficiency treated?
Treatment depends on the cause — some people need B12 injections, others can take tablets. Your clinician will advise based on whether the problem is diet or absorption.
Related tests
Other blood test investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Royal College of Pathologists / relevant professional body
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