Vitamins and minerals
Vitamin B12
B12 is needed to make red blood cells and to keep nerves working properly. The body stores it for a long time, so deficiency usually develops slowly over years.
Typical adult reference range
Roughly 200 to 900, with the low end often considered borderline · pg/mL
Ranges vary between laboratories and by age, sex and method. Always read your own result against the range printed on your own report.
What a high result can mean
A high B12 usually reflects supplementation. Unexplained high levels without supplements are occasionally investigated further, since B12 can rise with liver conditions and some blood disorders.
What a low result can mean
Low B12 can cause tiredness, pins and needles, balance problems, memory difficulty, and a particular type of anaemia with enlarged red cells. Causes include a diet without animal products, absorption problems, the autoimmune condition pernicious anaemia, and long-term use of metformin or acid-reducing medicines. Nerve symptoms can appear before the blood count changes, which is why symptoms matter as much as the number.
What commonly affects this result
Supplements, metformin, long-term acid suppression, a plant-based diet, and stomach or bowel surgery.
Questions worth asking your doctor
- Do my symptoms fit with this level, even if it is only borderline?
- Should we test for an absorption problem rather than just replacing it?
- Do I need injections or will tablets be enough?
See what your own results say
Upload your blood test and get a plain English summary of every value on it, with the questions worth raising at your next appointment.
Analyse my resultsThis page explains what a test measures. It is general information, not medical advice, and it cannot tell you what your own result means. Reference ranges differ between laboratories, and results are only meaningful alongside your history, your symptoms and your other results. Always discuss your results with your doctor.