The diagnostic approach to GERD distinguishes clinical (symptom-based) diagnosis from endoscopic evaluation based on the pathophysiological distinction between uncomplicated reflux and conditions requiring tissue-level assessment. Typical GERD symptoms (heartburn and acid regurgitation) have a positive predictive value of approximately 80% for pathological acid reflux, making an empiric PPI trial the most cost-effective initial diagnostic strategy — symptom resolution within 4-8 weeks effectively confirms acid-related disease. However, this approach fails to identify mucosal complications that alter prognosis and management. Endoscopy (EGD) directly visualizes the esophageal mucosa and is essential when alarm symptoms suggest complications: dysphagia indicates possible peptic stricture (fibrotic narrowing from chronic inflammation), Schatzki ring, or eosinophilic esophagitis; odynophagia suggests deep ulceration or infectious esophagitis; weight loss raises concern for esophageal adenocarcinoma; and GI bleeding or iron deficiency anemia indicates chronic mucosal injury. Endoscopy also enables biopsy for Barrett esophagus detection — the intestinal metaplasia (squamous-to-columnar transformation with goblet cells) that carries a 0.5% annual dysplasia risk and requires surveillance every 3-5 years (no dysplasia) to 6-12 months (low-grade dysplasia). Age >60 with new-onset symptoms warrants endoscopy because the incidence...