Decode my labs
Nutrient marker - Vitamin B12

What does a vitamin B12 level mean on your blood test?

Vitamin B12 helps your body make red blood cells and keep your nerves working. A low level can build up slowly and cause tiredness or other symptoms. Here is how to read your result.

Reported as
Serum vitamin B12
pg/mL or pmol/L

What the B12 test measures

Vitamin B12 is a nutrient your body needs to make red blood cells, support nerve function, and produce DNA. Your body does not make it, so you get it from foods such as meat, eggs, and dairy, or from supplements. A blood test measures the amount circulating in your serum.

How to read your result

B12 is reported in pg/mL or pmol/L, and the reference range can differ between laboratories. Because of that, whether a value counts as low is best read against the range printed on your own report and interpreted by your clinician. A borderline result is sometimes checked with additional tests.

What a low level can mean

Low B12 can develop from diet, from conditions that affect absorption, and with some medicines, and it becomes more common with age. Over time it can affect red blood cells and nerves, causing tiredness, weakness, or tingling. Your clinician decides whether a low result needs diet changes, supplements, or further testing.

See your own B12 explained

Upload your lab report and Mednex reads your B12 against the range on your own document, and tracks it so you can watch it over time.

Decode my labs
Free · educational, not a diagnosis · your data stays on your device

Common questions

What are signs of low vitamin B12?
Low B12 can cause tiredness, weakness, and sometimes tingling or numbness as it affects nerves. These symptoms have many causes, so a blood test and your clinician's interpretation are what confirm whether B12 is involved.
Who is more likely to have low B12?
It becomes more common with age and can affect people with certain digestive conditions, those taking some long-term medicines, and people whose diet is low in animal foods. Your clinician can advise whether testing makes sense for you.
How is low B12 treated?
Depending on the cause, it may be addressed through diet, oral supplements, or injections. The right approach depends on why the level is low, so it is a decision to make with your clinician.

Related guides

Hemoglobin, explained
Low hemoglobin and anemia
Ferritin, explained
Your iron stores and what low means
Vitamin D, explained
What a vitamin D level means

Sources

  1. MedlinePlus [Internet]. Bethesda (MD): National Library of Medicine (US); Vitamin B12 Level; [cited 2026 Jul 9]. Available from: https://medlineplus.gov/lab-tests/vitamin-b12-level/
  2. MedlinePlus [Internet]. Bethesda (MD): National Library of Medicine (US); B Vitamins; [cited 2026 Jul 9]. Available from: https://medlineplus.gov/bvitamins.html

Content last reviewed 9 July 2026. Reference ranges vary by laboratory; always read your results against the range printed on your own report.

This page explains a common lab marker in general terms using public information from the U.S. National Library of Medicine and other NIH sources. It is educational and is not a diagnosis or medical advice. Reference ranges differ between laboratories and the meaning of a result depends on your age, sex, medications, and overall health. Always discuss your own results with the clinician who ordered them.