Vitamin B12: Normal Range, High & Low Causes
What Vitamin B12 measures
Vitamin B12 helps make red blood cells and DNA and keeps nerves healthy. It comes from animal foods, so vegetarians, vegans and people with absorption problems are at higher risk of deficiency.
Vitamin B12 reference ranges
| Category | Conventional units | SI units |
|---|---|---|
| Low (deficiency likely) | Below 200 pg/mL | Below 148 pmol/L |
| Borderline | 200 – 300 pg/mL | 148 – 221 pmol/L |
| Typical | 300 – 900 pg/mL | 221 – 664 pmol/L |
Labs differ, and symptoms can appear within the borderline range. pg/mL and ng/L are the same number.
Need to convert units? Use the pg/mL ↔ pmol/L converter.
Common causes of a high result
- Taking B12 supplements or injections
- Liver disease
- Some blood disorders
- Kidney failure
Common causes of a low result
- Vegetarian or vegan diet without supplements
- Pernicious anemia and other autoimmune gastritis
- Metformin or long-term acid-reducing medicines
- Stomach or bowel surgery, celiac or Crohn’s disease
- Older age
- Heavy alcohol use
How to prepare for the test
Fasting is not usually needed, but some labs prefer it. Tell your clinician if you take B12 or multivitamins.
How often to retest
About 2 to 3 months after starting treatment, then as advised.
Track Vitamin B12 over time
Upload your reports and Labgist plots every Vitamin B12 result on one timeline, converts units and shows what changed.
Get the appFrequently asked questions
What is a normal vitamin B12 level?
About 200–900 pg/mL (148–664 pmol/L). Below 200 pg/mL is considered low.
What are signs of low B12?
Tiredness, tingling in the hands and feet, memory or balance problems, mouth soreness and anemia. Prolonged deficiency can cause lasting nerve damage, so it is worth testing early.
Can I have low B12 with a normal result?
Yes, when the level is borderline. Clinicians may check methylmalonic acid or homocysteine, which rise earlier when B12 is truly short.
Related tests
Sources
This page is general education and was last updated 2026-10-30. It is not a substitute for medical advice. See our editorial approach.