Acid-related and reflux-related tests are used mainly to diagnose acid reflux into the esophagus (the hollow tube that leads from the throat to the stomach). Tests may use a monitor on a small flexible tube (catheter) that is placed in the esophagus or a wireless acid-monitoring device that is temporarily attached to the lower part of the esophagus. People must not eat or drink anything after midnight before the test but are free to go home and eat and drink as usual after the monitoring device is placed. The devices are usually left in place for 24 but may be left in place up to 72 hours. Complications are very rare.
Doctors pass a thin plastic tube through the person's nose down into the esophagus. This tube stays in place for 24 hours. The tube contains one or more pH probes (pH is a measure of acidity). The probe detects acid that comes out of the stomach (called acid reflux) into the esophagus. Wires from the probe transmit findings to a data recorder worn by the person. The person records symptoms, meals, and sleep for 24 hours. Doctors match the probe data with the person's record of symptoms to see whether the symptoms occurred when acid was present. Some of the newer catheters also contain probes that can detect any liquid that comes out of the stomach, regardless of acidity (impedance testing). These newer catheters combine pH monitoring and impedance testing to measure both acid and non-acid reflux into the esophagus.
Doctors can also monitor acid in the esophagus using a wireless pH-sensing capsule. Doctors use a flexible viewing tube (endoscope) passed through the person's mouth to attach the capsule to the lower part of the esophagus. The capsule continuously monitors acid exposure for 48 to 72 hours and transmits results wirelessly to a receiver worn by the person. Thus, unlike the catheter-based test, people do not have a tube in their nose for the duration of the test. Similar to the catheter-based test, people record their symptoms, meals, and sleep for the duration of the test so that doctors can tell whether symptoms occurred when acid was present. The capsule does not have to be removed. It usually falls off within a week and is passed in the stool. Because the capsule transmits data wirelessly while attached, it does not need to be retrieved from the stool.