Area under pH 4: advantages of a new parameter in the interpretation of esophageal pH monitoring data in infants.

Twenty-four-hour continuous esophageal pH monitoring has become the preferred test to quantify acid gastroesophageal reflux. Agreement has been achieved that acid gastric content reflux into the esophagus constitutes a major cause of reflux esophagitis; we therefore calculated the "area under pH 4" (A) in 560 consecutive pH monitorings in infants 1-12 months old and related this parameter (A) to the reflux index (RI): RI less than 10%: A 185 +/- 295 (mean +/- 1 SD); RI 10-19%: A 1,046 +/- 1,206; RI 20-29%: A 1,967 +/- 2,038; RI 30-39%: A 3,307 +/- 2,955; RI greater than 40%: A 7,977 +/- 7,227. A higher RI is associated with a greater area under pH 4 (p less than 0.