What is it? The 24-hour pH, or stomach acid, monitoring test, also called the ambulatory 24-hour esophageal monitoring test, helps your doctor determine the factors related to your reflux and learn when acid enters your esophagus. A thin probe is inserted through one nostril and down your throat, stopping about 2 inches above the lower esophageal sphincter. The probe is attached to a wire connected to a small, lightweight box you wear on a waist belt. The box collects information about the number of reflux episodes you experience and when they occur. Combined with a diary you keep, your doctor will be able to tell if they occur when you're standing, lying down, sitting, or otherwise reclining. The advantage of this test is that you can continue your usual activities without interruption.

What is it used for? The 24-hour pH monitoring test is used for those whose symptoms continue but who don't have any evidence of damage to the tissues lining the esophagus. It can help your doctor determine whether symptoms are due to GERD or some other illness, such as heart disease or asthma. That's why the 24-hour pH monitoring test is often performed on those with less common symptoms, such as chest pain or respiratory problems.

What can I expect? Your doctor will ask you not to eat or drink anything after midnight the day of the test. You should also tell the doctor or nurse if you have had nasal surgery or a broken nose, since this may make inserting the tube more difficult. To avoid any discomfort, they will usually swab a numbing solution in the nostril where the probe is inserted, but you may feel the urge to gag as the probe passes through your throat. After it's placed, you can go about your regular activities, avoiding anything related to water, including bathing or swimming, which can damage the electronic monitor. While the probe is in place, you keep a written diary of the meals you eat, the time and type of symptoms you experience, what you were doing when symptoms occurred, and the position you were in. Even though the probes are very small, they can cause some discomfort in your throat or nose. Occasionally, this may persist after the test.