The area under pH curve: a single-figure parameter representative of esophageal acid exposure

This investigation aims at providing simpler methods for reading esophageal extended pH-metering tracings. Because the currently used parameters only quantify frequency and duration of acid exposure, we have measured the area between the pH curve and the pH 4 line (area under curve [AUC]) in an attempt to include in the evaluation the severity of acid exposure as well. We compared 20 control and 63 children with gastroesophageal reflux (GER). Extended pH metering curves were read according to currently accepted methods. In addition, we measured planimetrically total 24-hour AUC, AUC during daytime, AUC during sleep time, and total AUC excluding 2-hour postprandial periods. In spite of the very significant differences found between means of controls and GER patients for all variables considered, values overlapped widely. Receiver-operating characteristic (ROC) analysis indicated the best threshold values for differentiation of controls and GER patients and tested the diagnostic efficiency for each variable. We found that 24-hour AUC was the best comprehensive value (sensitivity = 1, specificity = 1) and that there was probably no use for fractional evaluation during selected periods of time. The optimum 24-hour AUC threshold value in the present conditions of measurement (paper speed, 0.25 cm/min; 1 pH unit, 2.5 cm) was 20 cm2. In order to facilitate comparison we propose using a pH-surface unit (pHSU) equal to recording speed (in cm/min) multiplied by vertical shift per 1 pH unit (in centimeters) (in this case, 0.25 x 2.5 = 0.625 cm2). A threshold value of 20 cm2 thus becomes 32 pHSU. A similar transformation will be adequate for any other recording conditions.(ABSTRACT TRUNCATED AT 250 WORDS)