<prompt> GERD is best diagnosed by?24 hour pH MonitoringUpper GI endoscopyBarium meal follow throughBarium Swallow  <response>: Ans. a 24 hour pH monitoringRef.: Harrison 19th ed. 261-2 Ambulatory 24-hour pH monitoring is the criterion standard in establishing a diagnosis of GERD, with a sensitivity of 96 and a specificity of 95. It quantifies the gastroesophageal reflux and allows a correlation between the symptoms of reflux and the episodes of reflux. However the diagnosis can be established on basis of Upper Gastrointestinal endoscopy with esophageal manometry. 