Chronic esophageal symptoms attributed to gastroesophageal reflux disease (GERD) are common presenting symptoms in gastroenterology, leading to high healthcare costs and adverse quality of life globally.1,2 The clinical diagnosis of GERD hinges on the presence of “troublesome” compatible typical symptoms (heartburn, acid regurgitation) or evidence of mucosal injury on endoscopy (esophagitis, Barrett’s esophagus, peptic stricture).3 With the growing availability of proton pump inhibitors (PPIs), patients and clinicians often utilize an empiric therapeutic trial of PPI as an initial test, with symptom improvement in the absence of alarm symptoms indicating a high likelihood of GERD.4 A meta-analysis of studies that used objective measures of GERD (in this case, 24-hour pH monitoring) showed that the “PPI test” has a sensitivity of 78%, but a specificity of only 54%, as a diagnostic approach to GERD symptoms.5 Apart from noncardiac chest pain, the diagnostic yield is even lower for atypical and extra-esophageal symptoms such as cough or laryngeal symptoms.6
The “nuts and bolts” of reflux testing
Ambulatory reflux testing assesses esophageal reflux burden and symptom-reflux association (SRA). Individual reflux events are identified as either a drop in esophageal pH to less than 4 (acid reflux events), or a sharp decrease in esophageal impedance measurements in a retrograde fashion (impedance-detected reflux events), with subsequent recovery to the baseline in each instance. Ambulatory reflux testing affords insight into three areas: 1) measurement of esophageal acid exposure time (AET); the cumulative time duration when distal esophageal pH is less than 4 at the recording site, reported as a percentage of the recording period; 2) measurement of the number of reflux events both acidic (from pH monitoring) and weakly acidic/alkaline (from impedance monitoring); and 3) quantitative evaluation of the association between reported symptom episodes and reflux events.
The SI and SAP can be calculated individually for acid-detected reflux events and for impedance-detected reflux events. Since reflux events are better detected with impedance, combined pH-impedance testing increases the yield of detecting positive SRA, especially when performed off PPI therapy.16,17 Because these indices are heavily reliant on patient reporting of symptom episodes, SRA can be overinterpreted;18 positive associations are more clinically useful than negative results in the evaluation of symptoms attributed to GERD.19 Despite these concerns, the two most consistent predictors of symptomatic outcome with antireflux therapy on pH-impedance testing are abnormal AET and positive SAP with impedance-detected reflux events.17