Comparison of stationary vs ambulatory 24-hour pH monitoring systems in diagnosis og gastroesophageal reflux disease
Twenty-four-hour intraesophageal pH monitoring is presently considered the most reliable diagnostic test for gastroesophageal reflux. Prolonged esophageal pH measurements can be obtained in hospitalized patients with a stationary technique and in ambulant outpatients by means of a portable device; however, there have been no studies that have examined whether the two approaches provide a similar diagnostic accuracy. We performed a prospective study to compare stationary and ambulatory pH-metry in the diagnosis of gastroesophageal reflux. Seventy-seven control subjects and 178 patients with proven gastroesophageal reflux disease were randomized to either ambulant or static pH-metry, which was performed with standard pH electrodes, sensors, and recorders. Reflux events (intraesophageal pH<4.0) analyzed were: number of episodes; total, upright, and supine reflux time; number of episodes lasting >5 min; and duration of the longest episode. A composite score of all reflux events according to DeMeester was also calculated. The limits of normality were defined as the 95th percentiles of the control groups. Both controls and patients assigned to either pH monitoring method were comparable. Of 255 studies attempted, 243 (95%) were completed successfully. The results showed similar median values of reflux events for the two control groups and for the two patients groups. Percent total reflux time provided a good separation between normal and abnormal reflux, with a sensitivity of 0.92 for static pH-metry and 0.68 for the ambulant procedure (respective 95th percentiles, 3.4 and 4.6). The lower sensitivity of ambulatory pH-metry compared to the stationary method could not be attributed to the higher normal limit in the former; circumstantial evidence suggests that dietary restrictions by the patients to minimize symptoms during home monitoring were probably responsible of this relatively high false negative rate. In conclusion, the results confirm the accuracy of stationary pH monitoring in the diagnosis of gastroesophageal reflux and show that the ambulatory procedure is less reliable; its sensitivity could probably be improved by strict dietary standardization.