Existing current tests for diagnosing GERD are suboptimal because they lack adequate sensitivity or specificity. Upper gastrointestinal endoscopy is highly specific for diagnosing GERD, particularly when erosive esophagitis is present (Los Angeles Classification B, C, or D). Nevertheless, its sensitivity is limited, as this scenario is only present in 30% of cases. Most patients will exhibit normal endoscopic findings, indicating Non-Erosive Reflux Disease (NERD). The 24-hour impedance-pH monitoring (MII) is currently considered the gold standard. However, its main limitation is that it can only measure reflux activity over a 24-hour period, in addition to the discomfort caused by the catheter. 6-8 It is noteworthy that 50% of patients with NERD will have pathological reflux, and the other 50% will have a sensory disorder. The importance of making an accurate diagnosis lies in the treatment, which varies in each case.11 Recently, a minimally invasive device was developed and validated in the USA to assess changes in esophageal mucosal impedance. This serves as a tool for evaluating tissue changes associated with chronic reflux. However, this device has recently undergone improvements. This new technology has not been tested yet for GERD diagnosis. The primary benefit would be the ability to diagnose GERD in symptomatic patients with NERD during the initial endoscopy conducted under sedation. Objectives The Main objectives of this study are to: 1. Evaluate the diagnostic performance of mucosal impedance measurement. 2. Investigate the mucosal impedance pattern in patients with and without GERD. Secondary objectives: 1. Evaluate the correlation between the global mucosal impedance measurement vs the first 3cm measurement 2. Evaluate the best probability score to distinguish between GERD and non-GERD Design Prospective, cross-sectional, and analytical study Study Design and Procedures The study will be conducted in the Gastroenterology Department of the Hospital de Clínicas José de San Martin, University of Buenos Aires, Argentina. Following a 4-week screening period during which a proton pump inhibitor (PPI) washout will be performed, and baseline measurements will be taken, all patients will undergo upper gastrointestinal endoscopy with mucosal impedance measurement and 24-hour impedance/pH monitoring.