Lab test glossary · Vitamins
Vitamin B12: what it means
Also known as: cobalamin, B12
Vitamin B12 is needed for nerve function and red-blood-cell production; deficiency can cause anemia and neurological symptoms.
What it measures
Vitamin B12 is essential for making red blood cells and maintaining nerves. It comes almost entirely from animal foods and requires a healthy stomach and gut to absorb, so both diet and absorption problems can lead to deficiency.
Typical range
Often roughly 200–900 pg/mL, though 'low-normal' values can still be symptomatic and are sometimes checked with additional markers.
Reference ranges differ between labs and are printed on your own report — always read your result against that range, not a general one.
What a high result can mean
- Usually supplementation; occasionally liver or other conditions
A high value is a starting point for a conversation, not a diagnosis — many causes are benign or temporary.
What a low result can mean
- Vegetarian or vegan diet without supplementation
- Pernicious anemia or other absorption problems
- Some medications (e.g. long-term metformin or acid reducers)
Why the trend matters
Because deficiency develops slowly, tracking B12 over time helps catch a downward drift before neurological symptoms set in.
When to talk to your doctor
A low or low-normal B12, especially with fatigue, tingling, or anemia, is worth discussing with your doctor.
Frequently asked questions
What are the symptoms of low B12?
Deficiency can cause fatigue, anemia, and neurological symptoms like tingling or numbness. Because it develops slowly, it can be present before symptoms appear.
What causes low vitamin B12?
A vegetarian or vegan diet without supplementation, absorption problems such as pernicious anemia, and some medications (long-term metformin or acid reducers) are common causes.
This page is general education about a common lab test — it isn’t medical advice and can’t interpret your specific result. What a value means depends on your history, symptoms, and the rest of your labs, which is a conversation for you and your clinician.