The results of ambulatory 24 hour oesophageal pH monitoring in 20 patients with established gastro-oesophageal reflux disease were compared with those of 20 healthy individuals with normal endoscopy. Cut off limits of pH 3, 4, and 5 were superior to pH 2 with respect to the discrimination of patients from normal subjects, and for the detection of pathological reflux. Using pH 4 as a cut off limit, the ambulant and recumbent periods of pH monitoring were more discriminatory than the postprandial period. Furthermore, it was possible to get complete separation between patients and normal subjects using several combinations of two reflux variables. Another group of 30 patients and 30 controls were investigated. Using percentage time at pH less than 4 as a single determinant of gastro-oesophageal reflux, the sensitivity and specificity were 87% and 97%, respectively, with 3.4% as upper limit for normality. Twenty four hour oesophageal pH monitoring in an ambulatory outpatient environment afforded clinically useful diagnostic accuracy in separating patients with gastro-oesophageal reflux disease from asymptomatic controls.
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