The Gastric Reflux Test (Multichannel Intraluminal Impedance Test) is performed to detect and record the amount of stomach contents coming back up into the esophagus when a child cries, arches, coughs, gags, vomits, has chest pain, etc. It also determines if the contents are acidic or not, how long they stay in the esophagus as well as how often this occurs.

A thin light wire with an acid sensor as well as six other sensors on it is inserted through the nose into the lower part of the esophagus. The procedure could be uncomfortable upon insertion but is generally painless.