The Gold standard investigation for Gastro-Oesophageal reflux disease is:
24 hour Esophageal pH recording provides a quantitative & sensitive documentation of acidic reflux episodes.
Disorders of Gastrointestinal System Including Diarrhea
Endoscopy
24 hour esophageal pH recording
Oesophageal manometry
Measurement of length of lower oesophageal sphincter
24 hour esophageal pH recording