Variations in results of simultaneous ambulatory esophageal pH monitoring.

Twenty-four-hour esophageal pH monitoring is regarded as the gold standard investigation for gastroesophageal reflux (GER) (1) and the possibility of an "incorrect" answer, false positive or false negative, is only rarely considered (2). However, when a group of infants in this hospital had such pH studies performed on two consecutive days, considerable differences in the results were found (3). This also had been reported from other centers (4-6). It seems likely that most of the differences were due to true "biological" variability in the amount of GER from day to day, but it remains possible that variation in the accuracy of the equipment in detecting acid reflux was also involved.