24-hour pH probe monitoring is a method for recording the amount and severity of acidic stomach contents backing up into the esophagus. This can be done on or off acid-blocking medication.
The actual test involves placing a small capsule at the end of the esophagus during an upper endoscopy (EGD). The capsule is able to record the acid levels in your esophagus over a 24-hour period and transmits them to a small moniter you carry around. Once you are connected to the monitor, you can go home and resume eating and normal daily activities.
During the test, you will record symptoms you have as well as routine activities such as eating and sleeping. Once the test is completed, your doctor can correlate these events with acid levels in your esophagus and make treatment recommendations.