The Gastric Reflux Test (Multichannel Intraluminal Impedance Test) is used to detect and record the number of times stomach contents come back into the esophagus and the relation of these episodes to symptoms (when a child cries, arches, coughs, gags, vomits, has chest pain, etc.). It also determines whether or not the contents are acidic and how long they stay in the esophagus.

The test is performed using a thin light wire containing an acid sensor, and six to seven metal sensors. It is inserted through the nose into the lower part of the esophagus. The impedance probe is then connected to a recorder box that the patient will carry with them for the duration of the study.