Your doctor inserts a thin, flexible tube equipped with a light and camera (endoscope) down your throat, to examine the inside of your esophagus and stomach. Test results can often be normal when reflux is present, but an endoscopy may detect inflammation of the esophagus (esophagitis) or other complications. An endoscopy can also be used to collect a sample of tissue (biopsy) to be tested for complications such as Barrett's esophagus. A monitor is placed in your esophagus to identify when, and for how long, stomach acid regurgitates there. The monitor connects to a small computer that you wear around your waist or with a strap over your shoulder. The monitor might be a thin, flexible tube (catheter) that's threaded through your nose into your esophagus, or a clip that's placed in your esophagus during an endoscopy and that gets passed into your stool after about two days.