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Abstract
Objective. Despite the new gold standard oesophageal impedance monitoring, pH monitoring is still used frequently for detection of gastro-oesophageal reflux (GOR). Besides drops in pH from above to below pH4, drops of ≥1 unit are also used as a marker for GOR. In this study the objective was to investigate the accuracy of drops in pH for detection of GOR, using impedance monitoring as the gold standard. Material and methods. Nineteen GORD patients (9 M, 55±11 years) underwent combined 24-h pH-impedance recording off acid-suppressive therapy. All drops in pH ≥0.5 pH units, with a duration ≥4 s, reaching the nadir pH within 5 s after onset were included. Reflux events detected with impedance monitoring were taken as the reference. Results. In total, 2221 drops in pH were found; 47% were acid (nadir pH <4), 47% weakly acidic (nadir pH between pH7 and 4) and 5% were superimposed (pH drop starting below pH4). The sensitivities of acid, weakly acidic and superimposed pH drops ≥1 were 91%, 28%, 24%, respectively, and the percentages of false-positive reflux episodes were 20, 56 and 54, respectively. Acid reflux with a cut-off ≥0.5 and ≤3.3 had a moderate-to-good sensitivity (94–70%) and low false-positive percentages (23–13%). In contrast, weakly acidic and superimposed reflux showed greater false-positive than true-positive percentages for all cut-off values. Conclusions. Compared to impedance monitoring, detection of reflux with pH monitoring is clearly inferior. When drops in pH ≥1 are used irrespective of nadir pH as an indicator of reflux episodes, the number of reflux episodes is overestimated. Decreases from above to below 4 with cut-offs between ≥0.5 and ≤3.3 are the most indicative of true reflux episodes.