Vitamin B12 Deficiency Anemia

Signs and Symptoms

  • Anemia
    • Fatigue, palpitations, skin pallor
  • Glossitis
  • Neuropsych
    • Symmetric peripheral neuropathy/paresthesias
    • Ataxia/gait abnormalities
    • Memory loss
    • Personality changes
    • Dementia


  • Drugs (metformin, PPI, H2 blocker)
  • Malnutrition
    • Alcohol use disorder
    • Dietary restrictions (low in meat and dairy products)
    • Elderly
  • Malabsorption
    • Gastric surgery
    • Crohns
    • Celiac
    • Fish tapeworm
  • Autoimmune gastritis (Pernicious anemia) most common cause
    • Dx: Anti-intrinsic factor Ab or historically Schilling test


  • CBC + peripheral smear (hypersegmented neutrophils)
  • Serum B12 Level +/- Folate
    • If normal/low-normal but still suspect (eg. macrocytic anemia), consider serum methylmalonic acid (MMA)
      • If serum MMA increased, suspect B12 deficiency


  • If cause not apparent, consider investigations
    • Consider testing for autoantibodies to intrinsic factor
    • r/o Crohns, celiac, etc...)
  • Vitamin B12 1mg (1000mcg) PO daily
    • Lifelong in pernicious anemia
  • Consider IM if concerning symptoms, poor compliance, or suspect pernicious anemia
    • 1mg weekly x 1 month then monthly IM or deep SC
  • Repeat B12 levels in 1-2d if concerning symptoms, or 2-4w if asymptomatic