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Gastroesophageal reflux disease (GERD) is a common disorder of the gastrointestinal tract characterized by the retrograde movement of gastric contents into the esophagus or mouth, causing discomfort or complications.[1] Population-based studies have identified GERD as one of the most common upper gastrointestinal tract disorders, with a prevalence of about 20% in the United States.[2] Patients may present with typical symptoms, including heartburn or regurgitation, or atypical symptoms such as cough, asthma, hoarseness, chronic laryngitis, throat-clearing, chest pain, dyspepsia, and nausea.[3] Typically, GERD is diagnosed clinically and treated with a trial of proton-pump inhibitor (PPI) therapy. Relief of heartburn and regurgitation after a 6- to 8-week trial of PPI therapy is a reliable indicator of GERD. This approach has a sensitivity of 78% and a specificity of 54%; hence, a negative trial does not rule out GERD.[4] However, this is a cost-effective approach to diagnosing GERD rather than proceeding directly to endoscopic or alternative diagnostic testing.[5] If patients present with alarm features (ie, new-onset dyspepsia at age greater than 60, gastrointestinal bleeding, dysphagia, odynophagia, weight loss, anemia, persistent vomiting), a trial of PPI therapy is not necessary, and the work-up should directly proceed to early endoscopy.[3] Ambulatory esophageal pH testing is performed using a wireless pH capsule or a traditional pH probe and is the gold standard for diagnosing GERD.[3] Some patients with typical or atypical GERD symptoms have a normal upper endoscopy and normal ambulatory esophageal pH testing but are unresponsive to standard PPI therapy. Ambulatory pH testing does not detect all types of reflux, especially when the refluxate contains little or no acid.[6] It relies on intraesophageal pH <4 as a marker of the presence of gastric contents in the esophagus to diagnose gastroesophageal reflux (GER) episodes. Hence, it has limited utility for detecting episodes in which the pH fails to fall below 4.[7]

Ambulatory esophageal pH testing is performed using a wireless pH capsule or a traditional pH probe and is the gold standard for diagnosing GERD.[3] Some patients with typical or atypical GERD symptoms have a normal upper endoscopy and normal ambulatory esophageal pH testing but are unresponsive to standard PPI therapy. Ambulatory pH testing does not detect all types of reflux, especially when the refluxate contains little or no acid.[6] It relies on intraesophageal pH <4 as a marker of the presence of gastric contents in the esophagus to diagnose gastroesophageal reflux (GER) episodes. Hence, it has limited utility for detecting episodes in which the pH fails to fall below 4.[7] A recent technique combining multichannel intraluminal impedance (MII) testing with pH testing enables detailed characterization of the refluxate, including its physical and chemical properties.[2] The MII detects the intraluminal bolus movement within the esophagus via the strategic placement of a catheter. It can, in combination with pH testing, characterize whether the bolus consists of liquid, gas, or mixed components, as well as its pH.[2]