Patients experiencing gastroesophageal reflux disease will usually need which procedure for a definitive diagnosis?

Upper endoscopy is the procedure most commonly used for a definitive diagnosis of gastroesophageal reflux disease (GERD). During an upper endoscopy, a thin, flexible tube with a camera is inserted through the mouth and into the esophagus and stomach. This allows direct visualization of the esophagus, where inflammation or other changes associated with GERD can be observed. The procedure can also facilitate biopsy if necessary, enabling the physician to rule out other conditions such as esophagitis or Barrett's esophagus.

In contrast, the other procedures listed have specific roles that do not provide a definitive diagnosis for GERD. Colonoscopy is primarily used for diagnosing conditions related to the colon and is not useful for examining the esophagus or stomach. A barium swallow test provides imaging that can show structural abnormalities in the esophagus but does not allow for the same level of diagnostic detail as an endoscopy. Esophageal manometry measures the function of the esophagus but does not provide visual information regarding mucosal damage or inflammation that can be indicative of GERD.