Vitamin B12
Overview
Vitamin B12 (cobalamin) measures serum levels of this essential water-soluble vitamin required for red blood cell formation, myelin synthesis, and DNA production via methylmalonyl-CoA mutase and methionine synthase activation. It is obtained exclusively from animal products and absorbed via intrinsic factor in the terminal ileum. Low levels indicate pernicious anemia, malabsorption, vegan diet deficiency, or metformin use, while high levels lack clinical significance; clinically useful for diagnosing megaloblastic anemia, monitoring replacement therapy, and screening at-risk populations for neurological complications.
Clinical Use Cases
- Diagnosing vitamin B12 deficiency anemia.
- Evaluating pernicious anemia (anti-intrinsic factor antibodies).
- Monitoring intramuscular or high-dose oral B12 replacement.
- Assessing risk in vegans, elderly, or post-bariatric surgery patients.
- Investigating unexplained neurological symptoms (subacute combined degeneration).
Specimen Types
- Serum.
- Plasma (EDTA).
Measurement Methods
- Competitive binding luminescence assay.
- Chemiluminescent microparticle immunoassay.
- Microbiological assay (functional reference method).
Test Preparation and Influencing Factors
- No fasting required.
- Recent vitamin supplementation falsely elevates levels.
- Folate deficiency masks B12 deficiency hematologically.
- Oral contraceptives, multiple myeloma may cause false elevations.
- Measure methylmalonic acid and homocysteine for confirmation.
Synonyms
- Cobalamin.
- Cyanocobalamin.