<prompt> The MOST sensitive test to diagnose GERD is:24 hour ambulatory pH monitoringUpper GI endoscopyBasal acid output measurementBernstein test  <response>: 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. 