Vitamin B12 deficiency

Etiology

  • Dietary deficiency (seen in vegans)
  • Decreased intrinsic factor production: pernicious anemia, gastrectomy
  • Competition for B12 in gut: blind loop syndrome, fish tapeworm (rare)
  • Decreased ileal B12 absorption: surgical resection, Crohn's disease, metformin
  • Pancreatic insufficiency
  • Helicobacter pylori infection
  • Transcobalamin II deficiency (rare)

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