A Crohn's disease patient involving the distal ileum should be monitored for malabsorption of which nutrient?

• A. Iron
• B. Calcium
• C. Vitamin B12
• D. Folate

Answer: (C)

Distal ileum involvement in Crohn's disease directly impairs absorption of vitamin B12 because this is the primary site where the intrinsic factor–B12 complex is absorbed. When the terminal ileum is diseased or resected, B12 absorption diminishes, leading to vitamin B12 deficiency that can cause megaloblastic anemia and neurologic symptoms from impaired myelin synthesis. Other nutrients listed are absorbed mainly in different parts of the intestine: iron primarily in the duodenum and proximal jejunum, calcium in the duodenum and proximal jejunum (and influenced by factors like vitamin D), and folate mainly in the jejunum. Therefore, vitamin B12 malabsorption is the most directly associated risk with distal ileal Crohn's disease. If deficiency develops, management may involve B12 replacement, with routes chosen based on the extent of absorption.