The Gold standard investigation for Gastro-esophageal reflux disease is:
b. 24 hour pH recording(Ref: Nelson's 20/e p1787-1788, Ghai 8/e p 280)Extended esophageal pH monitoring of distal esophagus, provides a quantitative sensitive documentation of acidic reflux episodes, the most important type of reflux episodes for pathologic reflux
Endoscopy
24 hour pH recording
Oesophageal manometry
Measurement of length of lower oesophageal sphincter
Gastro Intestinal System