<prompt> The best test to diagnose gastroesophageal reflux disease and quantify acid output is:EsohagogramEndoscopyManometry24 hr pH monitoring  <response>: The gold standard for diagnosing and quantifying acid reflux is the 24-hr pH test. -SabistonAlso, KnowUsing 24-hour pH test an overall score is obtained. It is known as the DeMeester score. 