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Impedance pH Test

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Gastroenterologists at Houston Methodist Lynda K. and David M. Underwood Center for Digestive Disorders offer advanced tests and treatments to help you gain relief sooner from acid reflux conditions.


The 24-hour impedance pH (nasal catheter) probe test monitors acid and non-acid reflux activity. This outpatient procedure allows esophageal specialists at the Underwood Center to evaluate how often stomach acid moves into the esophagus during a 24-hour period.


The test is most often prescribed for patients diagnosed with gastroesophageal reflux disease (GERD) who are not finding relief from acid-suppressive therapy such as proton-pump inhibitors (PPI). Your doctor may administer this test before prescribing acid reflux surgery.

World-Class Gastrointestinal (GI) Surgeons

Our multidisciplinary team at the Underwood Center offers state-of-the-art diagnostics and treatment for patients who need experienced esophageal care. Houston Methodist Hospital is ranked No. 5 in the nation by U.S. News & World Report for Gastroenterology & GI Surgery. U.S. News & World Report has also named Houston Methodist Hospital the No. 1 hospital in Texas every year since the award began and one of the nation’s best as a nationally ranked Honor Roll hospital.

Before, During and After the Impedance pH Test

How do I prepare for the impedance pH test?

Do not eat or drink after midnight prior to your test. Do not smoke the day of your test. If you’re an asthma patient, carry your inhaler.


Follow your physician’s instructions and discontinue the recommended medications seven days before the procedure.


Drugs such as proton pump inhibitors (AcipHex®, Prilosec®, Prevacid®, Protonix®, Nexium®, Zegerid®, Dexilant®) or H2 blockers (Axid®, Pepcid®, Tagamet®, Zantac®) may affect test results. If your physician instructs you to withhold these medications, but you experience discomfort, you may take these or similar antacids: Rolaids®, Tums® or Mylanta®.


Some patients may experience a nosebleed. You may drive yourself home after the procedure.

What should I expect during and after the Impedance pH test?

Testing steps:

  1. You are admitted as an outpatient, where staff will take your vital signs.
  2. Once the procedure begins, an esophageal motility test is administered to pinpoint the correct placement of the impedance pH probe. This involves inserting a very small catheter into the nostril and advancing it into the stomach.
  3. Your doctor slowly withdraws the catheter as you take sips of water. This portion of the test takes 20 to 25 minutes. After that the motility catheter is removed.
  4. Next your doctor inserts a different catheter, called an impedance pH probe, into the nostril and advances it into the esophagus. The impedance pH probe remains in place for 24 hours. The probe is connected to a small recorder you carry on a strap over your shoulder.
  5. Before you leave, we will give you information regarding diet, medications, smoking and bathing. We will also give you a diary sheet to record selected events throughout the 24-hour period. You will return the following day to have the probe removed.
  6. While the impedance pH probe is in place, some patients experience throat irritation. Take sips of water to help reduce irritation. Do not use throat lozenges, as they may affect the results of the test.


Some patients report more difficulty sleeping than usual because they are aware of the probe. Although the probe does not prevent eating or drinking, some patients find these activities somewhat uncomfortable. This discomfort typically lessens as you adjust to the probe being in place.

I am looking for advanced care or a second opinion?

We understand the concerns that come with acid reflux, GERD and heartburn. Whether you are looking for a diagnosis or a second opinion, we’re here to discover the cause of acid-related symptoms you may be experiencing.


The center’s compassionate team of gastroenterologists will test your symptoms and design a personalized treatment plan that works for you and your family.

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    Gastroesophageal Reflux Disease (GERD)

    GI specialists at the Underwood Center provide compassionate care and treatments for patients with GI pain or inflammation.

    Learn more about GERD >