Esophageal pH monitoring is used to diagnose heartburn and GERD. It is performed as an outpatient test and measures the pH of the esophagus. The pH of the esophagus indicates the amount of stomach acid that is in it.

A small probe is inserted into the patient’s nostril. It is positioned near the lower esophagus. The probe is then plugged into a monitor worn on a belt or over the shoulder. Over the next 24 hours, the probe and monitor record information such as the frequency of symptoms and the times that the patient eats and lies down.