TABLE 1.
Causes of megaloblastic anemia
| Etiology | Cobalamin deficiency | Folate deficiency |
|---|---|---|
| Nutrition | Strict vegetarianism or vegan diets | Malnutrition in elderly, alcoholics, impoverished communities |
| Gastrointestinal abnormalities | Gastric atrophy: achlorhydria | Celiac disease |
| Intrinsic factor deficiency – congenital or acquired abnormality | Dermatitis herpetiformis | |
| Total or partial gastrectomy | Tropical sprue | |
| Bacterial overgrowth in the small bowel (achlorhydria, anatomical defects, impaired motility) | Extensive jejunal resection | |
| Terminal ileal resection | Crohn’s disease | |
| Crohn’s disease | ||
| Extensive celiac disease | ||
| Zollinger-Ellison syndrome | ||
| Pancreatic insufficiency | ||
| Fish tapeworm (Diphyllobothrium latum) | ||
| HIV | ||
| Congenital defects (eg, Imerslund-Gräsbeck syndrome) | ||
| Drugs | Proton pump inhibitors | Cytotoxics (eg, methotrexate) |
| Metformin | Antibiotics (eg, nitrofurantoin, tetracycline) | |
| Phenformin | Anticonvulsants (eg, phenytoin, carbamazepine) | |
| Anticonvulsants | ||
| Cytotoxic drugs | ||
| Increased utilization/loss | Pregnancy | Pregnancy |
| Chronic hemolysis | ||
| Exfoliative dermatitis | ||
| Metabolic abnormalities | Congenital transcobalamin II deficiency or functional abnormality | Congenital folate malabsorption |
| Congenital intrinsic factor deficiency | Dihydrofolate reductase deficiency |