Ambulatory 24-hour esophageal pH monitoring with or without intraluminal impedance testing Impedance Planimetry (See also Manometry.) Impedance planimetry provides real-time assessment of luminal distensibility and geometric changes in response to applied pressure in various parts of the gastrointestinal... read more 
is currently the most common test for quantifying gastroesophageal reflux Gastroesophageal Reflux Disease (GERD) Incompetence of the lower esophageal sphincter allows reflux of gastric contents into the esophagus, causing burning pain. Prolonged reflux may lead to esophagitis, stricture, and rarely metaplasia... read more 
(see the American College of Gastroenterology's 2022 Clinical Guideline for the Diagnosis and Management of Gastroesophageal Reflux Disease). The principal indications are
To document excessive acid or nonacid reflux
To correlate symptoms with reflux episodes
To identify candidates for antireflux surgery
To evaluate the effectiveness of medical or surgical treatments
Ambulatory pH monitoring can be done when the patient is on or off proton pump inhibitor (PPI) therapy.
When monitoring is done while the patient is off PPI therapy, the diagnosis of gastroesophageal reflux disease can be confirmed or excluded. If monitoring is done while the patient is off PPI therapy and no acidic pH is found in the stomach, the diagnosis of achlorhydria is confirmed.
When monitoring is done while the patient is on PPI therapy, the adequacy of gastric acid suppression and the presence of esophageal acid exposure in patients who have been referred for testing because PPI therapy failed can be determined.
Tests may use a transnasal continuous reflux-monitoring catheter or a wireless pH-monitoring device that is endoscopically attached to the distal esophagus.
Complications are very rare. Patients must have nothing by mouth (npo) after midnight but are free to eat as usual after the monitoring device is placed.
Catheter-Based pH Monitoring
A thin tube containing a pH probe is positioned 5 cm above the lower esophageal sphincter.
The patient records symptoms, meals, and sleep for 24 hours. Esophageal acid exposure is defined by the percentage of the total recording time that the pH is < 4.0. If the time spent with pH < 4.0 is > 4.3%, this result is considered abnormal if the patient has not been taking a proton pump inhibitor, and a result > 1.3% is abnormal if the patient has been taking a proton pump inhibitor for the duration of the test. Additional sensors along the more proximal regions of the pH probe allow identification of proximal reflux episodes.
A dual-channel esophageal and gastric pH probe has two separate pH sensors along the catheter; one sensor is placed 5 cm above the lower esophageal sphincter, and one sensor is placed in the stomach. The two sensors allow for simultaneous measurement of the pH level in the distal esophagus and in the stomach. This test is most useful for evaluating the efficacy and adequacy of acid-suppressing medications.
The newer combined pH-impedance monitoring devices also do multichannel intraluminal impedance testing Impedance Planimetry (See also Manometry.) Impedance planimetry provides real-time assessment of luminal distensibility and geometric changes in response to applied pressure in various parts of the gastrointestinal... read more , which identifies reflux of any gastric contents into the esophagus regardless of pH level. In addition to acid reflux, this test helps detect weakly acidic reflux (pH between 4.0 and 7) and nonacidic reflux (pH > 7), which would be missed by conventional pH monitoring.
The correlation between patient-reported symptoms and reflux events can be assessed using the symptom index or symptom association probability. A significant symptom index value or symptom association probability value suggests that the correlation between symptoms and reflux events is not due to chance. Excessive reflux and significant symptom-reflux correlation are positive predictors of a favorable outcome from antireflux surgery.
Wireless pH Monitoring
Ambulatory esophageal pH monitoring can also be done using a wireless pH-sensing capsule that is attached to the distal esophagus.
The device is endoscopically placed 5 cm above the lower esophageal sphincter and continuously monitors esophageal acid exposure (defined as pH < 4.0) for 48 to 72 hours. Similar to the probe-based test, patients record symptoms, meals, and sleep for the duration of the test, and excessive acid exposure and symptom-reflux correlation (symptom index or symptom association probability) are identified. However, because the capsule is a pure pH sensor, only acid reflux is detected.
The capsule usually falls off within a week of placement and is spontaneously passed in the stool. The capsule transmits data wirelessly while attached and does not need to be retrieved.
More Information
The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
American College of Gastroenterology: Clinical Guideline for the Diagnosis and Management of Gastroesophageal Reflux Disease (2022)
