An ambulatory esophageal 24-hour pH study is an outpatient test that measures the amount of acid or non-acid reflux of stomach contents into the esophagus. The catheter placed in the esophagus measures acid concentration which corresponds to acidic reflux and impedance which corresponds to non-acid reflux. Symptoms will be analyzed for any correlation to episodes of reflux.

This is an important pre-operative procedure should be carried out before gastroesophageal reflux surgery. And also, as post-operative evaluation.