The Gold standard investigation for GERD is

(A) 24 hr pH monitoring > Useful investigations may include barium swallow X-rays, esophageal manometry, 24 hour esophageal pH monitoring and Esophagogastroduodenoscopy (EGD). In general, an EGD is done when the patient does not respond well to treatment, or has alarm symptoms including: dysphagia, anemia, blood in the stool (detected chemically), wheezing, weight loss, or voice changes. Some physicians advocate once-in-a-lifetime endoscopy for patients with longstanding GERD, to evaluate the possible presence of Barrett's esophagus, a precursor lesion for esophageal adenocarcinoma.> Esophagogastroduodenoscopy (EGD) (a form of endoscopy) involves insertion of a thin scope through the mouth and throat into the esophagus and stomach (often while the patient is sedated) in order to assess the internal surfaces of the esophagus, stomach, and duodenum.> Esophageal manometry is a test that measures the function of the lower esophageal sphincter and the motor function of the esophagus. A tube is passed down your throat until it reaches the esophagus. It is often performed along with 24-hour pH probe study.> In a 24-hour pH probe study, a thin tube is placed down into your esophagus for 24 hours.