<prompt> A 45-year-old lady presents with persistent reflux symptoms. The most accurate investigation in establishing diagnosis before surgical treatment includesEndoscopyAn UGI seriesEsophageal manometryAmbulatory pH monitoring  <response>: investigations for GASTROESOPHAGEAL REFLUX DISEASE, 24 hours oesophageal pH monitoring - the gold standard. PPI should be stopped for 3 weeks prior to pH monitoring. Barium study in head down position. Endoscopy to exclude other disease and to assess any mucosal injury - red inflamed mucosa often with ulceration. Sliding hernia can be identified through endoscopy. When patient retches, gastric mucosa will enter the OG junction and ascends upwards to variable distance. Ref: SRB;s manual of surgery,3 rd ed, pg no 723 