24-hour PH Impedence Monitoring

Thank you for choosing Tufts Medical Center's GI Motility Service. We have provided the below instructions to ensure that your time in our care is as pleasant and safe as possible. Please read all instructions carefully before your 24-hour PH impedence monitoring procedure as these directions are critical to your health and safety.

The procedure and what to expect

Your physician has ordered this 24-hour PH monitoring test. This test is used to assess the likelihood of gastroesophageal reflux disease and to determine the effectiveness of medications that prevent acid reflux. This study measures the amount of acid refluxing or “backing up” from the stomach into the esophagus (food pipe).

Esophageal pH monitoring is used in several situations to assess for gastroesophageal reflux disease (GERD). The first is to evaluate typical symptoms of GERD such as heartburn and regurgitation that do not respond to treatment with medications. The second is when there are atypical symptoms of GERD such as chest pain, coughing, wheezing, hoarseness, or sore throat. In this situation, it is not clear if the symptoms are due to gastroesophageal reflux. Occasionally, this study can be used to monitor the effectiveness of medications used to treat GERD. This study is often also used as part of a preoperative evaluation before surgery.

The nose is numbed for a short time. A thin wire-sized catheter is placed into one nostril, down the back of the throat, and into the esophagus as the patient swallows. The tip of the catheter contains a sensor that senses acid. The sensor is positioned in the esophagus so that it is just above the lower esophageal sphincter, a specialized area of esophageal muscle that lies at the junction of the esophagus and stomach and prevents acid from refluxing back up into the esophagus. Sometimes the probe has other pH sensors to measure pH in the stomach and in the upper esophagus and nonacid reflux using special sensors (impedance sensors). These extra sensors do not change the size of the small catheter. Placing the probe takes approximately 10 minutes. No sedation is necessary. The other end of the small catheter comes out the nose and is connected to a small battery recorder that is worn on a strap over the shoulder. The patient is sent home with the catheter and recorder in place.

During the 24 hours that the catheter is in place, the patient goes about his/her usual activities, for example, eating, sleeping, and working. Meals, periods of sleep, and symptoms are recorded by the patient in a diary and by pushing buttons on the recorder. The diary helps the doctor to interpret the results.


After the catheter is removed, the data from the recorder is downloaded into a computer and analyzed. There are very few side effects of esophageal pH monitoring. There may be mild discomfort in the back of the throat while the catheter is in place. The vast majority of patients have no difficulty eating, sleeping, or going about their daily activities. Most patients, however, prefer not to go to work because they feel self-conscious about the catheter protruding from their nose.

Planning for your appointment

The Tufts Medical Center GI Motility Service is located on the third floor in the Proger building. To find information on directions, parking and our campus map, visit the hospital locations and directions page >

Plan to spend about an hour in our unit for your procedure. We will do everything possible to avoid a delay, but emergencies may interrupt the schedule.

When preparing to come to the Medical Center for your appointment, please be sure to first:

  • Be sure you have an insurance referral, if required by your insurance company.
  • Be prepared to pay any co-payment on the day of your procedure.
  • Please bring the following items with you:
    • Your completed medical questionnaire and list of medication(s).
    • Your hospital card.

If you are unable to keep your appointment, please call us at least 48 hours in advance to re-schedule: 617-636-0142.