What to expect from ambulatory pH testing

Doctor writing a medical history
Laura Cox's picture
by Laura Cox September 19, 2012

What is ambulatory pH testing?

Ambulatory pH testing is the most definitive study for the diagnoses of GERD because it actually measures the reflux of acid into the lower esophagus. Most patients have never had this diagnostic test even though they are taking medications they will likely take for life. These are usually PPIs that have the potential for significant side effects when taken long-term. This is concerning since research has shown that approximately 30% of people taking PPIs do not have GERD, and thus are taking the medications unnecessarily. This test can definitively establish if GERD is (or is not) present. As a result, the patient can be appropriately treated or other conditions causing a patient’s symptoms can be investigated.

Oddly, the aggressive and frequent use of upper endoscopy represents the accepted status quo, even though 80% of those with GERD will have a normal EGD.  Remarkably, the pH study, which can be performed at the same time and with little risk, is rarely utilized by comparison, even though it is the best and most definitive study to make the diagnosis of GERD.

How is the test conducted?

For this test, a sensor is place in the lower esophagus that transmits “radio waves” to a pH receiver carried by the patient. The receiver is about the size of a cell phone and can be carried on a strap or on the patient’s belt. The actual pH study lasts 48 hours. During that time, the sensor detects acid refluxing into the lower esophagus and transmits this information to the receiver. Regular activities, including going to work, driving, and eating a normal diet, are necessary during the testing period in order to achieve accurate results. 

Since this study detects the acid component of the refluxing stomach juices, the patient must stop any acid-suppressive medications prior to the test.  PPIs must be discontinued for 1 week, but other drugs such as over the counter acid reducers (like Zantac, Pepcid or Tagamet) or topical antacids (like Tums or Mylanta) may be used, if needed, much closer to the time of the procedure.

There are two methods for placing the sensor:

  1. Telemetry capsule. An electronic capsule can be placed in the lower esophagus during the initial endoscopy. This adds approximately 10 minutes to the procedure.  Since the patient is sedated for the EGD, this placement is painless. Although coupling this study with EGD is optimal, the capsule can also be placed in a separate setting without sedation allowing immediate return to work and full activity without missing a beat. The capsule detaches itself, usually about 2 days after the test, and passes harmlessly through the body.
  2. Nasal catheter. Ambulatory pH testing can also be performed using a nasally placed catheter with an acid sensor on its end, but patients favor the telemetry capsule method.  The test period using this method is only 24 hours.  Less data is therefore obtained compared to the capsule method.  Also, the nasal catheter often inhibits a patient’s usual diet and daily routine.  The pH capsule described above has largely replaced the catheter method.  However, if you have a cardiac pacemaker, this catheter method must be used (as opposed to the telemetry capsule).

Whatever method is used, establishing the presence and magnitude of acid exposure to the lower esophagus, which definitively makes the diagnosis of GERD, is an essential part of an appropriate evaluation once symptoms reach an advanced stage.

After the 48-hour testing period (24 hours in the instance of the catheter method), the receiver is returned to the physician’s office and the information processed by computer.  The resulting report documents whether or not there is an abnormal amount of acid-containing stomach juice reaching the lower esophagus.  Put another way, the diagnosis of GERD is made or refuted. The result is the ability to provide treatment in a directed and logical way. Patients who are confirmed to have GERD can be treated properly and those without GERD can stop unnecessary medications or other therapies for a disease they do not have!

Reviewed by: Dr. Dengler, RefluxMD Medical Director

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