The Bravo pH test is the first catheter-free way to measure the amount of pH in your esophagus and is generally used to diagnose GERD. An endoscope is briefly passed through your mouth and into your esophagus to place a small gelcap that detects pH levels; the gelcap stays in place for 24 to 48 hours as you go about your daily activities. If there is a low pH in the esophagus, you may have GERD.