[Esophageal acid exposure in a single number: the area under the pH curve]

Current interpretation of pH-metering tracings takes into account several variables which indirectly reflect how many times and for how long time pH falls below a threshold value and how efficient is acid clearance. In this investigation we have tested the hypothesis that area under pH curve summarizes all the former values in one single figure. We have compared the four classical pH-metering variables (percentage of time under pH 4, number of GER episodes, number of those lasting more than 5 minutes and duration of the longer episode) and the area under curve between a group of refluxing children (n = 50) and a control group (n = 20). A value of 4% time under pH 4 was selected as "gold standard" for separation of both groups. We have figured out sensitivity, specificity and accuracy for all values of each parameter and, by means of ROC (Receiver Operating Characteristic) method, we have determined their performance and the optimum threshold value. Our results demonstrate that area under curve is at least as performant as percentage of time below pH 4, and probably better because it reflects, in addition, the depth of pH falls and the clearance. Taking into consideration that its measurement can be done automatically, we suggest that it should be included in the currently available software for computerized pH reading.