This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
The MOST sensitive test to diagnose GERD is: 
Select and explain. 
A. 24 hour ambulatory pH monitoring, B. Upper GI endoscopy, C. Basal acid output measurement, D. Bernstein test
A: 24 hour ambulatory pH monitoring
Answer: A: 24 hour ambulatory pH monitoring 
Explanation: Gastroesophageal Reflux Disease (GERD) Classic symptoms of gastroesophageal reflux are - water brash and substernal heaburn. Endoscopy is a sensitive test for diagnosis of esophagitis but will miss nonerosive reflux disease (NERD) MUST KNOW: The most sensitive test for diagnosis is 24-h ambulatory pH monitoring. Ref: Harrison, Edition-18, Page-2417.