Gastrointestinal and hepatic — PUD, IBD, cirrhosis, viral hepatitis
**Peptic ulcer disease:** H. pylori (most duodenal), NSAIDs (most gastric). Diagnose with urea breath test, stool antigen. Triple therapy: PPI + clarithromycin + amoxicillin × 14 days (or quadruple if clarithro resistance).
**IBD:** • **Crohn's** — skip lesions, transmural, anywhere mouth-to-anus (terminal ileum most), non-caseating granulomas, fistulas/strictures. • **UC** — continuous, rectum and colon only, mucosal/submucosal, crypt abscesses, toxic megacolon, PSC association (pANCA), cured by colectomy.
**Cirrhosis complications:** portal HTN (varices, splenomegaly, caput medusae, ascites), hepatic encephalopathy (NH₃, treat with lactulose + rifaximin), SBP (ascitic PMN ≥250, cefotaxime, prophylaxis with norfloxacin), hepatorenal syndrome, HCC (screening US + AFP q6mo).
**Viral hepatitis:** • **HAV** — fecal-oral, acute only. Vaccine (inactivated). • **HBV** — blood/sex/perinatal. HBsAg = infectious, anti-HBs = immune, HBcAb IgM = acute, HBcAb IgG = resolved or chronic. Treat chronic with entecavir or TDF/TAF. • **HCV** — blood (IVDU). ≥95% cure with 8-12 weeks direct-acting antivirals (sofosbuvir-velpatasvir, glecaprevir-pibrentasvir). • **HDV** — requires HBV coinfection. **HEV** — enteric, severe in pregnancy.
**Pancreatitis:** gallstones (most common), alcohol; lipase >3× ULN. Severe (Ranson/BISAP) — ICU, aggressive fluids, nutrition, imaging at 72 hr for necrosis. Antibiotics only for infected necrosis, not prophylactic.
**Colorectal cancer screening (USPSTF 2021):** start age 45. Colonoscopy q10 years, FIT annually, or stool DNA q3 years.