Vitamin B12
A vitamin needed for nerve function, DNA synthesis and red blood cell production.
| Typical reference range | 200–1,100 pg/mL |
| Commonly cited optimal range | above 500 pg/mL |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Vitamin B12 comes almost exclusively from animal foods and supplements. Absorption requires stomach acid and intrinsic factor from the stomach lining, and the liver stores several years' supply.
Why it matters
Deficiency causes macrocytic anemia, nerve damage (numbness, tingling, balance problems) and cognitive changes, and may become irreversible if untreated. Serum B12 between 200 and 400 pg/mL is a gray zone in which deficiency is possible.
What a high result can mean
High levels usually reflect supplementation or injections. Unexplained high levels can occur with liver disease, kidney disease and some blood disorders.
What a low result can mean
Low levels occur with vegan or vegetarian diets, pernicious anemia (autoimmune loss of intrinsic factor), reduced stomach acid (older age, proton pump inhibitors, H2 blockers), metformin, gastric bypass, Crohn's disease or ileal resection and nitrous oxide exposure.
What affects the result
Recent supplementation can mask deficiency. When results are borderline, methylmalonic acid (MMA) and homocysteine are more sensitive markers of tissue B12 status. Serum B12 can be falsely low in pregnancy and with folate deficiency.
Units and conversion
Usually reported in pg/mL.
- From pmol/L: multiply by 1.355 to get pg/mL
- From ng/L: multiply by 1 to get pg/mL
Also called on lab reports
B12, Cobalamin, Vitamin B-12, Cyanocobalamin, Vitamin B12 (Cobalamin), Vitamin B12, Serum
Related tests: Vitamins & Nutrients
This page is educational and does not replace advice from a healthcare professional.