A 55-year-old woman with prior ileocolic resection for Crohn's disease complains of abdominal bloating, flatulence, foul-smelling loose stools, and symptoms that worsen after meals. She has macrocytic anemia with a low serum B12 and normal folate. Which investigation best confirms the suspected diagnosis?

• A Fecal calprotectin measurement
• B Glucose hydrogen breath test showing an early rise within 90 minutes ✓
• C Anti-tissue transglutaminase IgA titre
• D Fecal elastase concentration

Explanation

Stagnant luminal contents after surgical blind loops predispose to small intestinal bacterial overgrowth, which deconjugates bile salts and consumes vitamin B12, producing steatorrhea with low B12 and normal folate. The confirmatory test is a carbohydrate breath test, typically glucose hydrogen breath, where an early hydrogen rise within 90 minutes indicates colonic-type fermentation occurring abnormally in the small intestine. Calprotectin reflects mucosal inflammation, tTG screens coeliac disease, and fecal elastase tests pancreatic exocrine insufficiency.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.