Vitamins
Vitamin B12 (cobalamin)B12
Cofactor for DNA synthesis and homocysteine remethylation; deficiency causes macrocytic anemia and neuropathy.
Sample
Serum
Clinical reference range
200 to 900 pg/mL
Adult
Conv: 200–900 pg/mLFunc: 500–900 pg/mL
Biology
What it measures
Bound to intrinsic factor in the stomach; absorbed in the terminal ileum. Stored 3–5 years in liver.
Clinical use
Why we order it
Diagnose macrocytic anemia, peripheral neuropathy, glossitis, dementia workup.
Lens · Clinical
Interpretation by lens
Clinical interpretation
Treat empirically when MMA elevated; oral 1000 µg/day matches IM in most patients.
Functional interpretation
Functional clinicians treat at <500 pg/mL with symptoms; tolerable upper intake is essentially unlimited (water-soluble, low toxicity).
Differential
Causes of abnormal values
Causes of HIGH
- ↑Liver disease
- ↑Myeloproliferative disease (high transcobalamin)
- ↑Active B12 supplementation
Causes of LOW
- ↓Pernicious anemia
- ↓Atrophic gastritis
- ↓PPI/H2-blocker use
- ↓Metformin
- ↓Vegan diet
- ↓Ileal disease/resection (Crohn's, bariatric surgery)
Pitfalls
Pre-analytic & interpretation traps
- !Borderline B12 (200–400) with macrocytosis or neuro symptoms → measure MMA and homocysteine — both elevated in true deficiency.
Follow-up orders
Logical next-step labs
Related