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Risk factors that should prompt consideration of B12 deficiency include advancing age (reduced stomach acid production), strict vegan or vegetarian diets, pernicious anaemia, gastrointestinal surgery (particularly gastric bypass or ileal resection), long-term use of certain medications (metformin, proton pump inhibitors, H2-receptor antagonists), nitrous oxide exposure (including recreational use), and conditions affecting the gut such as Crohn's disease or coeliac disease

What Is B12 Deficiency Anemia

When does persistent unexplained elevation justify evaluation for occult malignancy rather than interval observation

Pediatrics 2001;108(3):776-789