This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oesophagus, Subject name: Medicine
GERD is best diagnosed by? 
Select and explain. 
A. 24 hour pH Monitoring, B. Upper GI endoscopy, C. Barium meal follow through, D. Barium Swallow
A: 24 hour pH Monitoring
Answer: A: 24 hour pH Monitoring 
Explanation: Ans. (a) 24 hour pH monitoringRef.: Harrison 19th ed. / 261-2* Ambulatory 24-hour pH monitoring is the criterion standard in establishing a diagnosis of GERD, with a sensitivity of 96% and a specificity of 95%. It quantifies the gastroesophageal reflux and allows a correlation between the symptoms of reflux and the episodes of reflux.* However the diagnosis can be established on basis of Upper Gastrointestinal endoscopy with esophageal manometry.