Ambulatory 24-hour esophageal pH monitoring is a study in which continuous esophageal intraluminal pH measurement allows the detection of changes in pH caused by gastroesophageal reflux disease (GERD) episodes. GERD has a prevalence of 8% to 33% impacting all age groups and both genders. Acid reflux episodes are defined as pH drops to below four in the distal esophagus, and reflux time is the elapsed time until the pH exceeds four. Normal subjects do experience reflux episodes primarily after meals, but they are not associated with GERD symptoms. A physiological range of esophageal acid exposure has been established in normal subjects. Prolonged ambulatory 24-hour esophageal pH monitoring enables identification of both symptomatic and asymptomatic reflux events in physiologic conditions.

The value of the test lies in its ability to diagnose GERD in patients with normal endoscopic findings, atypical and extraesophageal symptoms, and poor response to medical, surgical, or endoscopic therapy, as well as in identifying patients who have an increased risk for a complicated outcome (prolonged nocturnal reflux, significant asymptomatic reflux).

Development of thinner pH probes and a wireless pH-sensitive capsule has made the procedure more acceptable to patients, allowing for data collection while patients pursue their everyday activities.

Reflux evaluation may be performed on or off proton-pump inhibitors (PPIs) therapy. To assess acid-exposure time in the esophagus, pH ambulatory monitoring should be performed off PPI therapy in patients without previous markers for GERD. If patients have previous markers for GERD, pH ambulatory monitoring should be performed on PPI therapy to correlate symptomology and refractory symptoms.

Multiple pH sensor probes allow the assessment of high-reflux episodes, involving the proximal esophagus and pharynx, as well as the simultaneous measurement of gastric pH if needed.

Multiple technology is available to place an ambulatory pH catheter. However, a recent study depicted the difference between using high-resolution esophageal manometry data versus the Air Flow Sphincter Locator to determine accurate pH catheter location. The data illustrated that the Air Flow Sphincter Locator was inaccurate over 30% of the time. Thus, using high-resolution esophageal manometry data is recommended to accurately identify the proximal lower esophageal sphincter (LES) border for proper pH catheter placement.