Gastroenterology and Hepatology Clinical Knowledge
Core concepts
Build a symptom-to-mechanism map rather than memorizing isolated facts. For upper GI complaints, distinguish mucosal injury (peptic ulcer disease, gastritis), motor disorders (gastroparesis), and acid-hypersecretion states (Zollinger-Ellison). For lower GI complaints, separate structural disease, inflammatory disease, and functional disorders. Know the alarm features that change a workup: unintentional weight loss, GI bleeding, dysphagia, odynophagia, persistent vomiting, iron-deficiency anemia, and new symptoms in older adults.
Understand the physiology behind the tests. Celiac disease testing requires the patient to be on a gluten-containing diet; tissue transglutaminase IgA is falsely reassuring in IgA deficiency, so pair it with total IgA. Fecal calprotectin distinguishes inflammatory from functional diarrhea but is nonspecific. H. pylori testing has a predictable false-negative problem with proton pump inhibitors and antibiotics, so hold them before breath or stool antigen testing.
Traps
Questions often swap timing and location: gastric ulcer pain is classically worse with eating, duodenal ulcer pain improves with eating but wakes patients at night. Another trap is confusing secretory diarrhea (large-volume, persistent with fasting) with osmotic diarrhea (improves with fasting). Chronic pancreatitis is a malabsorption and pain syndrome, not simply "low enzymes."
Rule of thumb
When a stem describes chronic diarrhea with weight loss and anemia, think organic disease and image or biopsy before labeling it irritable bowel syndrome. IBS is a diagnosis of exclusion only when alarm features are absent.
Worked example
A 45-year-old with bloating and diarrhea has normal colonoscopy and negative serology. Normal inflammatory markers and absence of alarm features support a functional diagnosis; persistent anemia would instead push toward small-bowel evaluation.