Which GI disorder is most associated with macrocytic (megaloblastic) anemia due to vitamin B12 deficiency?

• A. Crohn's Disease
• B. Ulcerative Colitis
• C. Diverticulitis
• D. Esophagitis

Answer: (A)

Vitamin B12 deficiency leading to macrocytic, megaloblastic anemia happens when B12 absorption is disrupted in the terminal ileum. The terminal ileum is where the B12-intrinsic factor complex is absorbed, so conditions that affect this area impair B12 uptake and DNA synthesis in developing red cells, causing macrocytosis. Crohn's disease often involves the terminal ileum, so it is the GI disorder most associated with this type of anemia. Ulcerative colitis mainly affects the colon, diverticulitis involves the colon, and esophagitis affects the esophagus, none of which typically compromise B12 absorption.