<prompt> Best method to diagnose GERD isOesophageal pH determinationEndoscopyBarium swallowLaparoscopy  <response>: 24 hours oesophageal pH monitoring is the gold standard investigation. PPI should be stopped for 3 weeks prior to pH monitoring. Dual probe pH monitoringone in distal oesophagus and one in proximal oesophagus is used to confirm the respiratory complication of GERD. Reference: SRBs Manual of Surgery, 6th Edition, page no 782. 